MTNZA took my hard earned money

I have a contract with MTN and they incorrectly double debited my account.I have followed up at a branch in Clearwater and still they haven't reimbursed me. The amount of money might be immaterial but the principle is that it is my hard earned money. I am feeling quite irritated right now and considering to change to another mobile provider that is more reliable. MTN just please treat me as a customer fairly and pay back my money!