Cancellation of contract

I sent the cancellation notice to the above mentioned service provider on the 4th February 2016 (Your service request with reference number *** has now been closed) they responded, and now I am doing a follow up why they saying my account will be billed until the 30th of April 2016, I am told that I need to serve the notice which I assume I did and the consultant from the billing department he and she put me through cancellation department and the phone was cutted off and no one bothered to call me back. Their services is so disgusting.