Billing beyond contract period

My contract was supposed to end in March 2015 but I was never informed nor reminded to upgrade. I then enquired during May and I was told that since it was in the last week of May, I must expect another billing by the 15 of June. They also assured me that my cell phone number has changed to prepaid. I was indeed billed for June and again in July despite my request to end the contract after they failed to notify me of the end date of contract.<br> <br> I then enquired again on the 17 of July but Joseph said he can't trace my number and promised to call me back again but never did until today. This company took over from Nashua Mobile and is now continuing billing me even beyond the contract period and is not keen to resolve this matter.