Fnb is becoming a ****

I tried writing e mail to Rahul Singh whereby he said I owe 6000 .so no response what im asking myself is why did my account showed a minus if I owned them i also use Absa I never had a problem with the minus 6000 but Fnb they make money out of us.which is not good at all.How can I have minus 6000 while I checked when I was using my money .