No understanding of the law

I had an account that was overdrawn and they had me blacklisted due to that. On 16 June 2017 I settled my account with them and I requested my account to be closed with immediate effect. Applying for motor finance, I discovered that I am still be blacklisted by them. The lady at customer support told me that I should send them a request for them to clear my name, but according to the credit report I still owe them the amount in question and hence I am unable to procure any loan and my credit record it blown to bits.