I want to change or cancel my DSL contract and cannot reach the customer service

I had an o2 dsl L 24 months contract that runs until the 8th of May. Apparently, and without my knowledge, this contract is extended for another year if it is not cancelled three months in advance. Now I am stuck with a contract for another year that costs me almost double the price of what o2 currently offers for the same service. I find this unacceptable, and a form of cheating. No, companies cannot simply say but you should know and get away with such behavior. I would happily switch to a company which treats its customers with respect.

So now, I would like to speak to the customer service, but three days in a row and after many attempts, I simply cannot reach them. "The queue is too long, call again later."

What should I do? I am already fed up with this unacceptably bad service. I cannot even cancel my contract via phone because I cannot reach them.