Being exploited by Telkom

My mother, a pensioner, cancelled her Telkom Mobile in May 2015. I even went into a Telkom store, got a reference number, ***8, and all was good to go. They billed her again in June, I phoned the call center again and they said that store only logged the request 1 June 2015. I told them that they needed to refund my mother and make sure that this account is now cancelled. They assured me it will be done, even confirmed my contact details with them, as they claimed they didn't have it, however on the cancellation form my number is on it. (her contract was over, therefore she only needed to give a months notice) We are now in August and they billed her again. I am livid, how can Telkom exploit a pensioner, she doesn't have an income and they keep on charging her. They need to refund all the money to her immediately. I work in a very big organization, and I will talk about the terrible way Telkom treats people. I am appalled. Telkom is the worst company and they ***** from their own clients.