There is finally a complaint against Deutsche Telekom about their, in my opinion, unfair peering practices (in German): https://epicenter.works/content/keine-zweiklassengesellschaft-im-internet-buendnis-reicht-beschwerde-gegen-deutsche-telekom-ein

It's a practice where they're trying to get money not only from their customers, who pay for internet access, but also from online services using very restrictive peering policies. The result is often that networks (and server owners) who don't pay Deutsche Telekom, experience connection issues with their users.

Keine Zweiklassengesellschaft im Internet: Beschwerde gegen Deutsche Telekom

Epicenter.works, die Gesellschaft für Freiheitsrechte (GFF), der Verbraucherzentrale Bundesverband (vzbv) und Stanford-Professorin Barbara van Schewick haben bei der Bundesnetzagentur eine Beschwerde gegen die Deutsche Telekom eingereicht. Ziel der Beschwerde ist es, Verletzungen des europäischen Netzneutralitätsgesetzes durch die Telekom zu beenden und die Internetqualität für Millionen von Telekom-Kund:innen zu verbessern.

I've experienced this first hand, back when I hosted a public Minecraft server. I had to pay my server host (Hetzner) extra, so that they would in turn pay for better peering with Deutsche Telekom. Had I not done that, a significant amount of my players would have not been able to play without lag.