My experience

I had the same situation with Columbia House. Someone lived in the same house forged my signature. I spent over an hour with them and got a copy of the original signed agreement. I found out the signature was not mine. I sent a lawyer letter to them explainning the situation and ask them to cancel the membership. It solved the problem.

The key was that they should have information as to how and when your membership started. If they can not produce any paper proof, you may have a case here. If they do, ask them for a copy and see whether you can remember that. If the operator can not help, ask for manager. Call them and be persistent. Their business is built on tactics like this and the fine prints. You just have to do whatever necessary on your side. It's also a good learning experience for me.