Overcharged by mobile phone company

I've just received my first ozone bill after transferring tona new operator and instantly noticed that I have been billed for calls to their customer service number amounting to a significant amount. As I was in Germany when I made the calls I am told that these are chargeable despite my protests that as the phone didn't work and should have i had no alternative but to call customer service in order to rectify it. I have found the whole process of moving to this new operator very stressful and to finally be told there is nothing they can do I feel very cheated. What are my alternatives? I had looked at small claims, and have heard about the oficina del consumidor but have ni real idea what they can do if anything.

 Spam post or abuse? Please let us know