New Contract already BS

I got a new contract from Cell C in May 2017, My first debit order was due on 20th of June 2017. On the 20th of June Cell C took their money but afterwards it bounced back. How is that possible when there is sufficient funds. This is the 3rd time now and I am getting fed up. I went to the bank and they can't see the ERROR. So this must be CELL C, I am switching to another network with better client services.

FIX THIS BS OF YOURS AND STOP DRAGGING MY NAME THROUGH THE MUD LIKE I CAN'T AFFORD!!