FNB Infrastructure problems

I pay my credit card in full on the 28th of each month. Been doing this for the past 20 years! If the 28th falls over the weekend, despite my paying my CC in full, FNB debits my chq account with the minimum payment required on the CC. I fail to understand how FNB calculates the minimum payment when: a) The is a zero balance on my CC b) I am paying my CC in full within 30 days each time. So I am not using the 55 day credit facility. FNB, would have you believe that the issue is yours and not their problem. Their call centre has now advised me that I should pay your CC 5 days before the due date, to avoid issues of this nature! This is a banking infrastructure problem! My chq account statement indicates a full payment was made to my CC on the 28th -two days before it was due! My CC statement indicates that a full payment was received on the 28th - two days before it was due. It is absolutely ridiculous that FNB refuses to acknowledge this issue or return the money debited back to my chq account! I have been told that I must do it via online banking and incur the relevant cost. FNB will then raise a claim internally, BUT a refund of the cost is not guaranteed! I need to change my bank...