Where's my money?

I have a Discovery Credit card which I pay in full by direct debit on a monthly basis. They took my fairly substantial payment on 29 September and here we are on 3 October and it is yet to reflect on my credit card account. I telephoned them and was told it takes up to 4 working days for a debit payment to reflect. What sort of banking system is this? Do computers stop working over a weekend? Where is my money? If I pay by eft today, it will be reflected in my credit card account tomorrow so what is the problem with a direct debit? Probably a money making **** by FNB to hang on to funds to make a quick buck on interest somewhere along the line.