Hours wasted. Service tech did questionable work. Online Tech support next to useless, operators don't read, seemingly don't have logs asking me to repeat myself constantly. Finally felt like i was getting somewhere and they changed to a different person who wanted to start troubleshooting again.

Background here. I pay for 800mbps service. Up till a couple months ago I used to get around that 500ish mbps down 20mbps up. I understood the limitations of the modem I had and thats fine. Then i started having intermittent drop outs, logs shown issues with the coax coming off of the pole to my house. Tech was dispatched, replaced the line but didn't secure it to the house properly and didn't remove the old cabling. He also added a surface mounted inline attenuator (we'll come back to this later) which he poorly drilled into my aluminum siding with 1 screw instead of removing the existing grounded couplers that were already attached to the house. At least the internet was stable, but now I couldn't get past 150mbps down. The tech suggested a new modem/gateway. Bought a new Netgear CM3000-100NAR as it was on the approved list, installed it and activated it download speeds remained roughly the same 120-140mbps down, but upload was quite a bit improved at around 180mbps. Decided to look into the status of the modem itself and noticed the coax was under voltage out of the normal acceptable range. Diag shows:

Downstream Status: Poor
Partial Service: Poor
Cable modem is in partial service mode. Your service provider might be under maintenance. Most of the time it won't affect your traffic and will automatically clear when work is complete.
Downstream Power Level: Poor
Downstream power is poor (-11.7dBmV). The recommended level is between -10dBmV to 10dBmV.
Downstream SNR Level: Good
Upstream Status: Good
Upstream Power Level: Good

This is when I noticed the attenuator that was added outside. I switched this back to the straight through grounded coupler and voltages were in the acceptable ranges again (rec is -10dbmv to 10 dbmv). Speeds still remained the same. Stable but not nearly as fast as they should be. Diag looks good though:

Downstream Status: Good
Downstream Power Level: Good
Downstream SNR Level: Good
Upstream Status: Good
Upstream Power Level: Good

Speeds remain roughly the same with a pc plugged straight into the modem or through the router/switch. No LAN issues present. All copper cables are CAT6A shielded (overkill) and tested with a Fluke meter to ensure they aren't an issue (I work with AV networks as part of my profession). Bottleneck appears to be something with Xfinity's lines in.

I decide yesterday to chat with techsupport trying to figure out the issue. I would post the logs here but the app refused to let me download them. We started off with an Op named "Sagar" who claims to see nothing wrong on Xfinity's end, and suggests I change service contracts as mine was older and "you can save money". I stated that I was already paying for 800mbps service and i don't see how changing to a different plan would fix the preexisting issue of underperformance. He insisted that it would fix the issue. OK, fine I ask for the terms that this new contract would have and also ask to remove my TV service since I haven't had a TV connected in several years. He says this isn't an issue and seemingly starts to prepare to get me the new contract and terms so i can read through it. Says I'll get $15 discount as well. Cool right? Wrong! None of this happens though. He sends me a link which i think is the info I wanted but turns out was just a FAQ on scheduling appointments, utterly useless info for what we were discussing. Right after this though the operator changes to "Vivek".

Vivek acts like I just started tech support and fails to acknowledge anything Sagar did the hour prior. Claims "I assure you that you have reached the right person". OK maybe he's the accounts rep to change the service? No he's just another tech support guy! I'm a bit agitated by this as he's now asking for info I've already given several times before trying to do the same thing Sagar already did. meanwhile I'm looking at the modem and not seeing any real signs of it being manipulated, you would expect a reboot at some point right? Regardless Vivek carries on acting like he's doing something, claims he's looking into WIFI settings.... Except, there isn't wifi on this modem. I state that as such. Claims I should just get a new Xfinity modem, but still says, "I know your modem isn't the problem." OK, then why did he suggest that??? He goes on for a few more nonsense things dealing with a home network that isn't there, changing my IP address ect. This has nothing to do with the issue and of course solves nothing. 11pm rolls around and I finally politely tell him I have to stop this troubleshooting as I'm out of time.

Checking logs on the modem, I only see signs of someone doing something at 9:15pm EST from about the time I was speaking with Sagar, and nothing after that. Lines show TLV-11, two DS profile changes, and a US Profile change. Won't post the actual log as it contains MAC info.

Also looking into the Modem the Downstream voltage is now slightly over the threshold, so something is happening with this line where the voltage is not stable.

Downstream Status: Poor
Downstream Power Level: Poor
Downstream power is poor (10.3dBmV). The recommended level is between -10dBmV to 10dBmV.
Downstream SNR Level: Good
Upstream Status: Good
Upstream Power Level: Good

I can plug it back into the attenuator but I feel like that won't solve the underlying issue and the voltage would like go under the threshold again when it fluctuates. Keep in mind this Line was fine for over 10 year prior to the issues over these past few months, and no attenuator was present then.

Regardless I've had several hours of my time wasted over this, spent money on a new modem only to get similar results and ran around in circles by so called "tech" support and as of typing this am still at 130mbps down.

At this point I wonder if I should be invoicing Xfinity for my tech support.