A customer service representative on Karl Marx Strasse in Berlin told me I wasn't going to be charged this month for DSL because of two mistakes that were made on my last bill that was over 220 euro.
I only got a refund for one of the two mistakes:
Einmaliger Anschlusspreis O2 DSL - 19.02.2020 19% 58,8151
Anschlusspreis Option AVM FritzBox - 20.02.2020 19% 42,0084
He said I wouldn't be charged this month to rectify the other charge. (And to check on my invoice because there might be a mistake again! HA!) It's true: I was still charged 85,34 this month. I demand a refund!