Fnb's terrible practice left me hopeless

Fnb's been running a pretty nice ****. I'm not sure of its scale. The **** is pretty simple. They don't process your purchases until you have less than the required funds. And then, they charge you so much extra for it. Recently, the ********* at Fnb have been doing this to me, consistently, even though I visited their branch and spent hours on the phone. Maybe because I'm a small-time businessman or maybe because they aren't scared of anyone. I don't know if other banks practice this sort of crime, if moving my account will help at all. I've grown to hate Fnb and I know I'm not the only one. I just hope they get what's coming.