Charged incorrectly for transactions

I have a private wealth account with FNB, when making purchases online the monies are not banked immediately but a few days later when FNB processes. At the same time the monthly account management fee goes off and now FNB charges me a fee as if they paid for the original transaction. I queried this with the manager at private Wealth and she tells don't make purchases or do any transactions on your account until such time that the fees have gone off and if on the weekend then i must wait till the next business, i asked her if the bank can stop backdating it would also assist but obviously that will not be the case, she also tells me that i must take out a overdraft facility to cater for these item but its already catered for with sufficient cash when making the purchase. This has now happened several times with this useless bank and seriously considering leaving this bank. I will also be taking this up with the Ombudsman.