Too quick to charge additional fees, unfair treatment

I have a business cheque account with FNB, on this account an Afrihost debit order goes off on the 1st of every month. I had made provision for this debit order to go off on the 1st of March, just to find that it didn't go through and I was debited with an "item unpaid" fee by the bank, which is close to double the amount that was supposed to be debited. The supplier also charged me an additional fee due to this inconvenience. I then realised that the monthly account fee was deducted from the account, also on the 1st, before my D/O went through. Now how can I be penalized because the bank took their portion before my D/O??? This does not make sense at all and I was extremely disappointed by it, still am. Surely the monthly fees could've just pushed the account into a minus which would then be recovered with my next deposit. I want a reversal on the unpaid charge because irrespective of the fact that the account is in good standing, it was still a setback on my budget and that was not my fault because I provided specifically for the D/O to avoid unpaid bank charges. I would appreciate a prompt response.