Failure to Refund

I have a contract with Cell C. I called them some time this month to change my banking details, the lady who assisted me told me the new banking details will only reflect next month and advised me to make a cash deposit for this month. I deposited cash to their account on the 20th of this month, later on that day I got an sms notification that Cell C debited my new account. I gave them an allowance of a day for payments to reflect then called the following day for a refund. I was told to wait 3 days then I will get the refund, until today I've been calling them and every time they lie and say they tried to contact me. I sent them an email this morning up until now I have not received any response. This service is unacceptable because when you miss payment by just a day, you have to pay charges but now that they are on the paying end, I must run after them for my money.