It's worthwhile complaining as high up as possible. I had troubles with CC, bought a sat dish etc. I complained and took it as high up as I could, each time someone told me I couldn't go higher I asked them to cancel my subscription there and then.

Eventually I got a manager who was really nice to be honest, I had them offering me all sorts to stay on as a customer. So, if you are locked into a contract, see what you can get for free while you're at it.

Complain and thou shalt receive.