Charge without authorization

I December 2020 I opted for swap Over to “pay as you go” after over 10 years of a contract agreement. I visited an Mtn store and an agent assisted me with raising a reference number to carry out the instruction. I was told that someone would call me to complete the downgrade. I never received a call. I sent an email to Retentions with a confirmation to have the downgrade actioned. I kept following up with Retentions, then customer service when and finally emailed Complaints. Needless to say, I received no response. And so Mtn kept billing me as per the contract I had formally cancelled. I finally had the “pay as you go” 3 months later !! And when asked for a refund on the basis of all the communication I had sent over the period of 3 months and yet again, I’ve had no response from neither Retentions, Customer Service nor Complaints for 3 weeks now.