Failure to process cancellation of contract

On 31.12.2015 I submitted a cancellation form for two contracts that had completed their term. In early Feb I received a large account due end Feb. I went in store on 4.2.16 to query the account. Desre assisted me and told me that no cancellation had been processed. The consultant who had originally assisted me said he had no recollection and suggested that I had not given him a cancellation form whereon I gave him the date and time of my visit. I completed another cancellation form and was assured that I would receive a response in 4 days. I have since been back to the store, called several times, sent an email, called the call centre twice and have spoken to a consultant from the contract department, all I get is promises to get management involved and have someone call me. I have even requested a response by email as I am not always available by phone. To date I have not received any response. I would like to have both contracts put on to prepaid in order to change to another service provider that offers a better service and more area coverage. This problem has not been resolved and my account is about to be debited with this large amount. I require urgent intervention.