Refusal to close my acount

I have a STD Bank acc which I can't maintain. The acc is currently owing and I take full accountability for that and I admit that I need to pay it. I went to the bank to have it cancelled and will pay the outstanding amount in 3 months. They refused to close the account and said I need to pay it first. The acc is on negative balance and every month there are bank fees and penalties being charged because of the negative balance. If I can't afford to settle it now then what's going to happen if I won't be able to pay for the next 6 months?? I can't afford the current owing amount but then you expect me to settle a larger amount in future that it is now??? How is this possible?? Please contact me for arrangements. The amount keeps going up. I won't be able to afford it hence I need to close the account now while still at the current balance.