Unable to close or settle account

I paid up my account in December and requested the account be closed. I was informed my account was in credit and banking details requested for money to be refunded to which I submitted immediately. Upon numerous times following up on the account closure I was assured the account would be closed and I would be refunded. Only to be informed that my account has now accumulated interest and I owe the bank money and therefore my account cannot be closed. Consultants at the bank and over the phone are unable to assist leaving me in a position where I am unable to close my account and am still being charged daily interest