Very bad service.

Good day, My account number was GRO ********** (ZNP018128), I cancelled this service in June 2015, I was then told that I had to give 3 months notice, I paid until the end of September 2015. I then received an account for October, November and December 2015. I have now been handed to Debt collectors which I do not think is right. Furthermore if this has been placed on my credit record I would like confirmation that it has been removed.