No help changing ownership from deceased grandmoth

Contract is under deceased grandmothers name. She died in January and I have been trying to get the contract cancelled since. Two months ago I paid the outstanding amount in order to cancel the contract and phoned in to have it cancelled but just got transferred from department to department. I was finally told to email my query to an address for escalated queries. I got one reply weeks later and nothing thereafter. The account is still being billed and now they want another payment. All I wanted was to keep the number I am using but Cell C really is not helpful.