Over debiting my bank

MTN is over charging people!!!! This is unacceptable. On the 1st of October they deducted R3400.00 instead of R299.00 Been on the phone(Call center) and branch since the first, no refund has been paid to me. They keep saying my query has been escalated to the billing department. Today the 22nd of October 2020 (same month) they deducted R599 again. I am worried that they will deduct again month end on top of all the amounts they owe to me. How do I stop them from debiting my account?