FNB Charges for unpaid Items

This is happening again. I have been charged R 630 for items paid no funds. It says there 6 items paid but no funds in the account. The items are speed point transactions that I did when there were funds in my account and because the merchants did not update their speedpoint transactions on time( According to FNB) I am now being charged. Suprisingly when swipe mu card, the money is moved to pending transactions. So what happens to the money when the merchants finally present their speed points. The total of the transactions in question is only R 385 but the bank charge is R 630???????