FNB making my life a living hell

The only reason i stopped banking with FNB was due to an over draft limit, i remember i once called to reduce the limit from 5000 to 1000,however today i find myself owing FNB 6000 although i had asked for a reduction on the limit, anyway here's my story.... FNB handed my account to debt collectors, Blakes and associates for not paying the owed amount of 6000, i agreed to an arrangement of R200 every month and made my intentions clear with FNB that i want to close the account, i was advised that the account will only be closed after the full amount has been settled... Now i receive a call again from Blakes saying the R200 i pay is too little since the monthly premium is more than R200(premier cheque),, i was astonished as i thought once i start paying, interest won't accumulate as I'm no longer using the account and have stated that i want to close it and was told that i can't close it until all payment has been done. I find myself not progressing with the account... As they keep adding and adding and adding. Please advise as to what is to happen as I'm now considering to block the debit order and stop paying altogether