Withholding money from my account

I was not able to set a limit on my credit card internet banking, so I had to pay in a huge amount at the end of the month, now that the money is deducted they deny me access to that amount. I need an explanation, most of all I need to understand why that certain amount was deducted. I also need to have access to my account at all times after an FNB assistant promised the money will be released this morning.