Mtn price hike

Last year, one of my contract came to an end and I was paying R1180 per month including a cellphone and data plan. On the 27 November 2023, Mtn deduced R2666 and no reason why and I called mtn immediately to investigate the high cost. The case was opened and till today, there has been no refund and this month Also, I see an invoice of R2666. I tried to call and upgrade my contract and till to-date there isn't any network.