MTN STOLE MY MONEY

So I have tried to do the honorable thing, and deal with MTN directly, but they just seem to be ignoring me. Basically my contract was paid up, 4 months later I switched to prepaid only two find out that during the paid up period and me switching to prepaid, they were still charging me for the device (that I already paid for in full), I have logged several cases (***,***,***), spoken to several call center agents and spoken to their so called \help"on Facebook and still nothing. I was told that I would be refunded"