Incorrectly put an arrears flag on my account

I'm very disappointed with FNB, I tried to use my revolving facility and I couldn't upon enquiring I was told that one of my accounts was in arrears, which was a very big surprise for me. Then I asked which one and when, I was told my premier cheque account was in arrears on the 6 Sept as a result of electricity purchase, I believe there's clearly something wrong with FNB systems because before I make a purchase there will be balance available and the amount get reserved Pending clearance of the transaction, it is also important to note that I don't have an overdraft facility I use what is shown as balance available, how then do I get penalized for this? I believe your system is just a mess because also on the same day 6 September, there was money deposited in my account and I was able to continue using my account on other transactions even after the 6th. I request that you please remove that arrears flag on my account because this was obviously not the case.