Billed for a cancelled contract once again???

I cancelled my contract yet Vodacom still billed me for a handset fee. On the 1st of January 2019, I called the call centre and spoke to a Team Leader by the name of Theo. He acknowledged the error and said they didn't cancel my contract on time and I will receive a credit. He said he will get an agent from the accounts department to call me in the 2nd of Jan to process the credit. It is now the 12th of Jan and I am still waiting for that call!!! Vodacom did the very same to me when I.cancelled a contract few months back. It seems like you enjoy *****ing from your clients !!! If there are any competent staff left at Vodacom can you call me to have this resolved ???