Canceled account, still being billed

Hello,

We left Germany over a year ago now. We still had money left to pay on the iPhone we took with one mobile contract so carried on paying it. Now I want to check how long is left on the contract to pay, or just to arrange to outright pay anything left, BUT I can no longer log into my O2 account as I don’t have the number linked to the account anymore as the German o2 contracts have been cancelled.
Can I please get some help in sorting this out?