A simple transaction that went terribly wrong.

I made a cash deposit into my standard bank account at Pick & Pay. When I checked my balance I was shocked to learn that my account has a overdraft (which I don't have on my standard bank account) of the exact amount I had just deposited at Pick & Pay. My account is now in the minus. Which means I now owe the bank. I contacted Standard Bank, the customer service operator didn't have a clue what I was talking about. After a lenghty explanation I was told to hold. After a while he came back on the line, indicating that he was not aware Pick & Pay and Standard Bank offer the service. I'll have to go back to Pick & Pay to sort it out. Went back to Pick & Pay the manager explained that everything was correct on their side plus my receipt was indeed a deposit slip. Which had a minus before the cash amount I deposited. According to Pick & Pay management that is how their receipt is. Needless to say they said it will reflect in my account in 24 hours max. Although my Standard Bank account states AVAILABLE BALANCE - (minus) R***xx. Now I see they have taken funds for being in arrears. I'm stuck with no money and a overdraft after depositing cash. How is that possible??