Standard bank not clearing my name - Experian.

I'm a prestige client for Standard bank and yet I have received the worst service from them. Even the so called banker that's supposed to be helping me with my needs has been useless. I have asked them a numerous times for a paid up letter or to clear my name at Experian for a credit card account I closed back in 2018.Experian (credit beuorex) is still reflecting the account as open and is also showing an outstanding balance which is impacting my credit score negatively. I now want to buy a house and cannot get Standard bank to clear my name with Experian or provide me with a paid up letter, so that I can follow up with experian. I've been thier customer since 2007 when I started working and now I'm doubting If I should continue with thier service, seeing that they don't take care of their customers.