Tymebank- poor service to SASAA pensioner

I am a SASSA pensioner. I went to Spar to buy groceries - The transaction was declined even though I had enough funds. So I went and drew cash to pay for my groceries only to get home and find the transaction had been debited from my account- effectively meaning I paid for the food twice. On enquiring with Tymebank they said it would take over 30 days to refund me- how can this be? I have proof of the decline and cash payment and that the funds were also debited - they are prepared to leave an old age pensioner without money for food for the month- this is disgusting- through not fault of my own! Disgusted.