Poor service Rentions Dept Cell C

Its more than a year ago I requested CEll C to cancel my contract after it expired . I went to Cresta office to inform them of my cancelation request I was at Mall of Africa I contacted there call centre and instructed them to cancel the data sim card. Now they telling me I am using the line when I don't even have the sim card I gave them instruction that no calls are allowed and no excess billing is allowed when I took out the contract they have been billing me for more than 16 months now they billing me for call usage on watsapp. I don't know if the rentions department is stupid or don't they know how to run there business. Cell C wake up stop *****ing funds from innocent ppl