My elderly parents in Perth have got phone/internet issues that they can't figure out, and it's causing them to miss important doctor's appointments - who could I send around to get it figured out once and for all??

I hope this is the right place for this! I looked on Whirlpool for an appropriate place but it was all so specific. It could be a skill issue, they're super old. I wish I was there to help.

They've been on the phone to Telstra for so many hours for months, and nothing ever changes - I'm sure you all know what that's like!

It's a kinda weird problem:

• Outgoing calls on both the landline and one of their mobiles goes fine for a few minutes and suddenly that they can no longer hear anything but the other person can hear them just fine. This is consistent and always happens.
• Their other mobile seems to work just fine.
• Incoming calls seem sporadic and messages are mostly not received.

Fwiw:

• They were having huge problems with spammers, so they've got some sort of old Telstra landline-phone that they like that cuts down the spam calls.
• I don't know what sort of Internet they have, they say they have a white telstra modem that's about 5 years old (sounds like a "smartmodem" I guess). I think it plugs directly into the phone socket.
• They're unfortunately occasionally tricked into clicking/installing some stuff they shouldn't.

I have a suspicion it's either:

• some setting they've enabled themselves,
• or to do with Wi-Fi calling and the modem, maybe one of the cell phones has Wi-Fi calling enabled and the other one doesn't
• or the modem or the landline are not working properly.

...but I have no way of checking from overseas.

So yeah, is there someone I could send around to just work with them and get it done?

From googling I see various suggestions, but none of them sound like they'd actually just be able to help to old people figure stuff out?