In the mean time I've solved my problems with a crack, so I can play offline. I understand there could be some discussion about how legal it is to do that, but I think Monte Cristo did not uphold the EULA by failing to provide me with a working account and support. That way, I don't think I am obliged to comply with the EULA myself and I am free to solve the problem myself. As soon as they can fix the problem I will play the game the normal way, but I don't see that happening very soon.
The other option would be to return the game to the store and get a refund, but I think it benefits the developer (or whoever owns Cities XL now), the store, the other users
