This. A thousand times over.Ask around and choose a provider who has a good track record for fixing problems when your connection dies. Budget providers tend to be pretty listless in that respect. A couple of weeks without broadband is a right pain,
I know. I've used Talk Talk and Plusnet.
This is in the UK, but I use Andrews and Arnold. I could save money and go for a company that is cheaper, but it's worth it for proper knowledgable technical help.
I used to use Plusnet and signed other people up to the extent where I got free broadband. Which was useless! When it went wrong, I was on the phone for hours and hours. First day with my current ISP and the broadband hadn't come on. I was dreading another call but the first person who picked up the phone took my details and said "ah, I see - I'll sort this out and send you a text when it's working". Everyone who works there is an expert.
I am sure there's a German equivalent.