Money deducted out of my account for a vodacom mistake.

Vodacom deduct money from my account for contract that's been canceled prematurely but was canceled a month in advance now struggling to get money back from vodacom. I contacted vodacom and they said sorry they made a mistake and the amount of money would be refunded in 7 days, still waiting have a reference number why must I wait 7 days for my money that they made a mistake for and they are still not keeping to te agreement.