Du kannst bei der Hotline einen Umsatzsteuerbeleg anfordern.

https://www.o2online.de/kontakt/

Hello @gardenduck,

welcome to our o2 Community

you can request a free sales tax receipt from our customer service. It is created retroactively for each individual month. The creation of the invoice and its dispatch are free of charge.

The easiest way to do this is by phone or in our prepaid chat: Kontakt. Of course, you can also request the receipt in writing, the address is:

Telefónica Germany GmbH & Co. OHG
Kundenbetreuung
90345 Nürnberg

Please let us know if you have any further questions.

Best regards

Gulia