Supersonic Reneges on their part of contract

For the last year or so i have not had much of an issue with Supersonic. That changed this month. I have received an email from their billing dept. informing me of an increase to my premium. Whilst i accept and understand that increases must happen every year, what really ****es me off is their intent to increase my premiums by 100%. I have signed up with them because of the special they had run at the time, but now their intention is to renege on their part of the agreement and increase my premiums for the same product they are offering me. Calling them and sending them messages are a complete waste of time and money as they blatantly ignore and disregard any communication with them to account for their actions.