@Nadig first read here. If you have any questions, post here again. Did you a 24 months or Flex contract?

https://hilfe.o2online.de/english-o2-community-broadband-dsl-70/how-to-do-a-cancellation-of-my-dsl-contract-due-to-moving-abroad-508314

Hi Joe, Thank you for the help offered.

I have 24 months contract. When i had checked in o2 shop in Essen, they mentioned that if i submit the De registration letter, they will immediately terminate the contract. Now they are telling me to send the termination letter and de registration copy to the 90345 Nürnberg address. I have only few days left in Germany. Could you suggest any quick process to get the contract terminated? Also could you advise how to check my Kunden Number? i am not able to seet it in the contract document or the monthly invoice email. Is there a customer service email where i can send the docs?

@Nadig look here what an official o2 moderator say to the required documents one day ago.
 

I think you have an rented o2 router. Don’t forget to send back over the o2 dsl return portal oder you must pay a penalty payment.

Hello,

My contract was terminated in August 2020. However I've been getting Invoice that I can't even see anymore, because portal always show error.

I had also written letter to terminate along with De Registration and Flight ticket details. I even returned WiFi Router to O2 mentioned address. 

Now I have received another invoice for September 2020 that I cannot see. My written requests to O2 to terminate are ignored and continue to be debit the amount from my Bank Account.

I ask for help on this matter.

Hi @Nadig 

I have sent you a private message via our @o2_Support User,

there we can go into detail regarding your contract and last invoice. 

Best Regards Matze