BAD SERVICE DELIVERY

I HAVE BEEN TRYING TO CANCEL A SMS SUBSCRIPTION BILLED TO MY ACCOUNT WHICH I HAVE TRIED TO CANCEL SINCE OCTOBER 2014 AS MY NUMBER HAS NOT BEEN IN USE SINCE SEPTEMBER 2014. AND I HAVE TO PAY FOR IT! ASKED MANY CONSULTANTS NOT TO CALL ON MY CELL PHONE AND USE LANDLINE BECAUSE THEIR NUMBER CUTS OFF ON MY CELLPHONE. SO THIS HAS BEEN CARRYING ON SINCE OCTOBER AND STILL BILLED TO MY ACCOUNT. HOW DIFFICULT CAN IT BE TO CONFIRM WITH CELL C THAT THE NUMBER HAS NOT BEEN IN USE SINCE SEPT 2014 AND THEREFORE THE AIRTIME COULD NOT HAVE BEEN USED??? WHY CANT THEY CALL MY LANDLINE AND GET THIS CANCELLED AND CREDIT MY ACCOUNT - FOR I HAVE NOT UTILISED THE AIRTIME AND HAVE CANCELLED FIVE MONTHS AGO?