Complain about Rechnung: chargning due to automatic activation of Game and Musics Paket

I have a O2 contract with fixed monthly tarif. But, I have noticed recently that O2 has activated since 6 months automatic activation of Game and Musics Paket without my request and request!! They already charged me more than 200 Euro for this service (monthly >30 Euro). I have visited the O2 shop in mediamark which I signed my contract. I told them how this can happen, but they had no real answer. They just said sorry and only deactivated the serivice! I asked them for procedure for returning the addtional cost, but they asked me to call O2 hotline. They already mentioned it is highly unlikley that they reurn my money. I would like to start a case against them. I treid several time to call O2 hotline but always long wating time. Before talking to my lawyer about this issue, I would like to know if already someone has this experinece? Can someone help with preparation of a complaint letter to O2. 

Any help is greatly apprecited.

Thank you and best regards