Changing internet contract owner or cancelling contract

Do you not want to use your connection at the new address?

I already have internet here that works and is from my flatmate. I do not need it.

For some reason, the MyO2 page doesn’t let me access my contract information. It always takes me back to the homepage whenever I press any button. I’ve tried multiple browsers and it simply does not work. Do you have a link directly to this page where I can input the information of the new contract holder? Or is there a way I could do this via email?

Register with your landline number.

I don’t know my landline number (we’ve never used it) and I don’t live in that flat anymore. My current landline is used by my flatmate as it is her flat so I do not want to use it. I need another way to cancel my contract or change the holder of the contract.

The landline number is listed on every invoice and included in the order confirmation. There's no other option. You can cancel at the end of your regular contract here: https://info.o2online.de/kuendigung/

Hallo ​@aly25 ,
welcome to our o2 Community 😀
Please do as Bumer writes. 
Either search for your phone number and initiate the contract holder change online or cancel the contract. 
Alternatively, you can also call the hotline so that your colleagues can initiate the change of contract holder for you. 
Our English-speaking postpaid and landline support for you: 089 66 66 30 08 1 
(Mon. - Fri. 8 am - 8 pm, Sat. 10 am - 6 pm, on workdays)
Kind regards, 
Solveig