MTN refuses to fix their errors

I'm so angry and disappointed with Mtn. I have 2 contracts with them yet their service delivery is utter *******. On 27October I bought R99 airtime via my banking app and apparently MTN had problems with crediting airtime. I've phoned them every week for the past 3weeks with no solution. I've emailed them my proof of transactions and notifications from my bank but still they refuse to credit me with the airtime I paid for. They keep giving me reference numbers and referring me to the bank but I've sent them proof that the transaction was successful. I'm so sick and tired of their *********** and I cannot wait to leave their network. My money has gone down the drain and I'm just fed up I wish there was a way of reversing my transaction. R99 is not small money in this day and age