contract no cancelled at end of 24 months

I have a 24 month contract I assumed at the end of the 24 months the contract would be cancelled but find out that they continue to debit order you without your consent I phoned and phoned and got cut off three times after trying to cancel I was on the phone for 15 minutes each time and then got cut off then they give me an email address which is invalid get your management to sort this out my contract number is ***