Inkompetenter Kundenservice.
I filled out their moving form (Umzugsformular) but they incorrectly created a new internet contract for my new address so I paid double for over 3 months until I noticed the extra charges.
I then reached out to their support team, which seemed quite effective and promised me a full refund in the next bill. However, once the new bill arrived, the amount that should've been refunded appeared as an extra charge. I blocked the SEPA order and got an automatic email asking the incorrectly billed amount to be paid in 3 days or extra fees would be charged.
I've sent over 5 emails now but they are only responsive via phone calls. They have refused to speak English in 2 out of 5 calls. They also hung up on me in another call as I was explaining the issue.
After managing to speak broken German in one of the calls they appeared to understand the issue but decided to apply the owed refund on the bill that was listing the refund as an extra charge - therefore giving me no refund for the mistake they made by creating a new contract when I moved.
I have now sent them one more email saying that if the problem is not solved I'll have no option but to contact Schlichtungsstelle der Bundesnetzagentur and Verbraucherzentrale. I can't understand how they try to get away with ignoring emails and miscalculating customer bills after multiple mistakes on their side.