MTN SA won't give me my money back

Bad experience with MTN SA. I had a cellphone contract with MTN of which I paid monthly via eft. I was paying it upfront and happened that I paid +R700 more of the total amount of the overall contract. I contacted MTN and they have been saying they will send me back my money since December 2019 and it is now April 2020. They always say we will send it within 14 days. Poor customer service and satisfaction.