Extremely unhappy client

I paid my mtn contracts in store as I did not have money in my bank account for a debit order. When I received my money in my account Mtn still debit my account even though I already made payment. Kindly please refund my money and also cancel my contract as It is very hard, or rather impossible to contact your call center as well as retentions. the phone rings for hours on end and email enquiries are not responded to.