Mtn refund

Late last year l received a call asking if l wanted to update/upgrade my data package. Do l did. A month later my account was debited nearly three times my normal amount. No amount of calls or even a visit to my local mtn shop has rectified the error. I left Mtn for many years due this lack of desire to do refund. Cell C never gave me this problem. Mtn has lost me as a client.