MTN INCORRECT BILLING

Hello Peter Iam Bayanda Bizana I have a challenge with Mtn in Queenstown I took a contract on the 22 December 2020 amounting to R349.00 monthly and I have softlocked the phone to my surprise they deducted R6 972.27 from my account, I went to the store to enquire about that and I was promised that the response will take 4 days. I waited and they were always telling me a new story saying its with the billing department and another surprise in March they deducted R12 789.00. They said I must reverse that from the bank. They told me that billing Department agreed that billing was incorrect, they said I must pay in cash my monthly installment and they removed the debit order option until the problem is solved. I asked for a written letter explaining ing that as that has ruin my Fnb account (credit score). The are delaying the whole process and its frustrating me. Please assist as I have to contact them all the time to get feedback.