DSL contract termination

I am leaving Germany at the end of March, so I need to terminate my O2 DSL contract.

I was told to phone a number, and it would be taken care of in that way. Unfortunately when I called and typed in my 'Festnetznummer' (as requested), I was told the number was not recognised, and the call ended.

I tried a different number (as given by an assistant on the 'O2 Hilfe' Facebook page) and waited 30 minutes to be connected, at which time my credit ran out - and so the call ended.

I was then told the best way to terminate my contract would be to fax O2, which I did yesterday. Shortly after I sent the fax, I emailed O2 to ask for confirmation, but they didn't reply. I emailed again this morning, but they still haven't replied.

What can I do now? Why do you make everything so difficult?