MTN Over Charging Calls and not resolving the matter!

I recently moved to a new area having been using Vodacom all along, now this area has no 4g signal for Vodacom or Fibre except for MTN, I then bought a MTN SIM which works well in this area, except for that I've been enormously billed for calls, going anywhere between R3.50 per Minute to R5 instead of the 79c per minute Call Plan I chose. For roughly 3 months I've been overcharged. I then called the Call-Centre and they verified that indeed this is the case, they escalated the matter for me and gave me the Reference Number, promised me a refund within 48 hrs, that was on the 1/8/2019, it's the 14th August still nothing, when I call all I get is that the matter hasn't been attended to as yet, including today. Very Disappointing for a 1st time user.