Just a thought. Is the phone case station connected to the phone socket via a micro filter? If you have a broadband connection, all phone sockets that have a phone connected need one,not just the one the router plugs into. It'll be something like this:

https://www.amazon.co.uk/ADSL-Filter-Broadband-Plusnet-Vodafone/dp/B004AEYHNI

Fthu7
May 2023

But, beg or borrow another phone and try that. If the problem goes away it was your phone. If the problem persists, it might well be the line, so you can then get your provider to sort that, telling them you have eliminated the phone as a culprit.

Fthu7
May 2023