FNB (no funds for 560 debit order but -798 for items unpaid)

Alright FNB here we go again. So everytime you guys try to debit Cell C which only costs R560 from my account that does not currently have the funds and than put a minus R105 for for items unpaid. Has now accumulated to my account being on minus (-) R798 .. Which could have already paid my cell c account. Please stop this nonsense!!