Does anyone have a solution for my constant M-net interference?

I'm a customer of m-net. Until October, I lived with my ex-boyfriend for a year in a flat on the outskirts of the city. Because I'm self-employed and working from home, sometimes I just can't hear the radio anymore and start a series on Netflix.
In short everything works, then every minute of stream needs 5 min to load.
Say, I can't load or watch / play.
The same thing happens with my mobile phone. No internet, no stream possible.

I've called hundreds of times at m-net, nobody can help, everything is on their side. I have changed radio channels and almost built an aluminum panel for the router (housewife tip of an employee).

Now I moved to a city apartment in October. My new roommate also has m-net and no problems with it.
What good news!

No, on the contrary. After a short time it turned out that I have exactly the same problems here in the city as on the outskirts.
Interestingly, my roommate hardly has them.

What is the problem? Does anyone know? Especially since I have the problem on mobile and PC.

I'm very happy about answers

First of all a few questions:

Is that cable or DSL, which router and you have a wireless network for your phone and PC?

This is DSL and both devices are in the same WLAN.