Take over DSL contract of customer who can't login

Hello, 

I would like to take over a DSL contract from one of your customers, but we have a problem. He can't login to his account to change the contract ownership. He doesn't have his “Nutzername” nor his “Rufnummer”. O2 says his email address is incorrect (even though it’s the one that’s registered with his account, apparently). But he has all other important personal information, such as the pin number. Neither of us can speak German very well, so that's why I'm using this channel instead of calling the hotline.

Could you reset his password or give him his account number and landline number? I can also give you his mobile number and email address so you can reach him directly if there are privacy concerns.