Tell them that you will be terminating your service with them at the earliest opportunity....you will have their retentions manager on the phone offering you all sort to stay with them.
They started throttiling my bandwidth so I left them, they offered me 1 years free BB, i still told them to shove it, they actually said and I quote "what have we got to do to keep you as a customer ?...reply "stop throttling my service"... answer " I cant do that" ...reply ok goodbye then.....6 years later thewy still write to me begging me to come back