Fnb making me drown in debt

I moved to Capitec a few years ago, my fnb account was on minus so i could not close it. I joined debt review. We made an agreement with FNB on how il pay their remaining balance on the cheque account. All my debit orders were cancelled. To my surprise i now owe -R4900 on my cheque account. I posted a complaint a while back and i was given a huge document which does not solve my issue. I refuse to pay this amount because i don't know how it got to be this much. I was a client for so long and never gave problems, why am i now being given more debt when i am already drowning? So customers are only treated well when their finances are intact?