Need help understanding what supervisor is saying. Won't let me switch one of my cell phones with another phone I've purchased because of an old internet acct?

I have an xfinity mobile acct. I previously had an xfinity internet account but disconnected last year. Before that was disconnected, I had asked them to put the service on hold in April of 25 because we would be out of town for several months. They said they would do that. Upon returning in August, we learned that had never been done. At that point the bill was over $700. They told me they would fix it but basically wanted me to pay for it first, which I was not willing to do because I didn't trust it would be fixed and it didn't make sense why I needed to send my money in order for them to fix their mistake. That bill has been sitting like that ever since, even though I've tried numerous times to fix it.

Now for the present..I have a phone that hasn't been working. I have no service unless I am using wifi calling. (Through a different provider) I called xfinity and they tried to figure it out. If I try to make a call elsewhere, it says I have no service and data won't work either.

So I went through with tech support for hours last night trying to figure it out. They were unable to. I was still on the phone with them and they kept asking me to login to my xfinity online and I did that just fine but then they wanted me to open a certain tab, it wouldn't open (even though all other tabs opened just fine). They asked me to do this repeatedly over 10 minutes and the process of the phone "thinking" took my battery from 25 to 0% pretty fast and it eventually disconnected after having spent that long trying to fix it.

Today, I started looking at replacement phones. I could get one through xfinity and it would cost me $1899 I want to say, split up into payments. Or I could drive an hour and buy one from a guy for $450. Of course that's the route I want to go.

Before doing that, I wanted to double check if the phone was compatible etc so I called and gave the IMEI number. They confirmed it was compatible but said I was unable to switch it because I no longer had an address associated with the account because originally I had the wifi and then ordered the mobile phones after.

So because there's no address linked (which is ironic because it has me verify my address every single time I call), they are telling me I can't switch out a phone that they can't get to work, with one I've purchased on my own. Make that make sense.