Faulty Credit Card transaction not declined

We have business and do a lot of card transactions, last week we did two sales the customer paid with a Credit card we used the chip on the card to do the transactions , it then asked for a authorization code which the customers put into the machine, and the payment was approved, now STANDARD BANK refuse to give the money, the sales was approved on the card machine,Standard bank customer service is saying that we had to phone the bank , WHY how are we suppose to know you need to phone the bank if a transactions is approved?? REALLY how reliable is Standard bank if they approve card transactions if there is no money on that card or the card is *******, from Standard bank side how can you just say we had to phone the bank , it's YOU as a bank's responsibility to DECLINE a card if there is a fault with the card or there is no funds available how can you say that it's our responsibility how are we as the customer suppose to just know this things , we are now R20 000 missing and Standard bank refuse to take responsibility for their mistake?? How helpful is that?? This is YOUR mistake FIX it !! Contact Johan to sort out this problem