Unable to cancel , my line is held hostage

I would not recommend this provider to anyone, we have been trying to cancel with them for months now but it's impossible to get hold of them. we were resorted to chat with them online a this is the best way to get service, but even if you ask the questions, you get computer like answers from the agents you talk to as they completely ignore the questions you ask, every time there is something new as to why they can't cancel. We gave them December as a calendar month notice, but now they say that they can't find that reference even if I sent it to them twice now. I do not want another collection to go off in Jan, but if we do not pay, they keep your line hostage and you are unable to get another provider I am very unhappy with the service they provide