Changed transaction dates to fill own pockets

I was charged an insufficient funds bank charge because FNB decided they were going to process some of my payments on days they felt like it. I had various transactions happen in a 3 day period which didn't fit into FNB's schedule (and budget) so they conveniently processed some transactions early and others late so they could charge me a reversal fee for a debit order that was processed. The transactions that happened to interfere with this debit order, according to FNB, happened to be processed on Sunday, after the debit order date of Saturday. How can you process transactions that happened on a Sunday a day early to suit your needs and so that you can claim insufficient funds? Now I have to contact that company and explain to them why your **** has negatively affected me, never mind the further repercussions of this against my name. You better fix this!