I have a stand alone garage card which is paid in full every month

I have a stand alone garage card which is paid in full every month. As usual payment went off via debit order on 28 April. On Sunday my card said limit exceeded which is not possible. Today I enquired and was informed that the monies paid on the 28th has still not cleared and evidently the amount I paid through debit order is all of a sudden R700 less than the amount they received. I queried same via email but still awaiting a response. Who is to pay for the interest as from date payment was deducted and where is the rest of my payment and why have I not received a courtesy call to inform me that payment was not allocated yet or that a problem incurred. Sloppy service Standard bank.