FNB'S PATHETIC

I have had an FNB Credit Card for over 40 years. Every month, for more than 4 years on the 25th an amount in excess of R5000 is deposited to my account. Yet they block my account because I did not make provision for an interest payment of R307 - how on earth is this possible. When I queried it, their only response was "the system". For crying out loud - how can the system not pick up that that regular payments are made to this account and that this is a GOOD account on which I have NEVER been in arrears????????