Data being charged for 3 years and no refund

I have a contract with Vodacom for +- 10 years and previous to my recent upgrade, I had an iPhone contract, this came with a data charge special for 3 months at R218.oo per month for 1gb, it was meant to fall away after the 3 months promotion but was charged to me up until July 2018. I have many times contacted Vodacom and went in to the store to rectify the problem, I have spoken to Supervisors and no such luck in refunding me my money which amounts in the thousands. It was confirmed in January by a Vodacom Solutions employee that in the range of R5000 was to be refunded to me and was out of his budget to authorise, I have been ever since calling and emailing for the problem to be rectified and refunded. Vodacom has given me reference numbers and also sent more notifications that my query was resolved. They have refunded me R1000.00 but that is not the entire amount that needs to be refunded. I have had no joy from calling or emailing Vodacom to date.