Incorrect amount deducted from bank account

I upgraded to My MTNChoice 2GB @ R89 per month, on 11 May 2017. On 31 May 2017 MTN deducted the amount of R1288.27 from my bank account. I complained at the Saveway Crescent branch in Witbank and received an email on 15 June, confirming that it was a mistake and that I will be refunded by MTN (REQ ********** ). Despite numerous enquiries, I still haven't received any refund after 4 months.