FNB so called digital banking is a mess and technical errors costing clients

For the past few months I noticed that Nedbank MFC debit order from my private cheque account was being rejected. I did not pay much attention as I though maybe I have used more money than planned. I made arrangement for Nedbank to debit twice in the following month. This happened every month now, September and October same thing happened. I decided to check my bank statements.

From the bank statement it seems FNB has messed up my bank account. I get paid on the 25th monthly and my debit orders are set for the 26th. On the 26th there will be a sufficient amount on my account to cover my debit orders but this particular FMC debit order is rejected even though I have enough money on the account. How can a debit order be rejected when I have more than enough on my account to cover all debit orders?

Now this mean , FNB has been billing me for rejected Debit Orders , it also means MFC is not getting money which is messing up my credit profile. I am also concern that my account has errors that could mean i have lost some money.