Requesting to get the available contract over me.

Hi, I just moved into my new apartment in Freiburg. The former tenant has already home internet, and I wanted to get the current contract over me. Even if we tried to change the contract details together through her account, it didn't work. Just bank details changed, and the rest is still the same ( former tenant personal infos etc.) Could you please help us with this issue? how can we overcome this problem? I just want to continue to use the current contract.