Refusal to give paid up letter

FNB handed over my credit card account as it was in arrears and I worked hard to remedy that situation. I have since paid up and they now are ignoring my emails to send me a paid up letter, prior to this it was a struggle for them to update payments accordingly, the owing amount would not match the payments and statements were not sent timeously. On FNB’s side I am still in arrears yet I have styled the debt with their chosen debt collector. The last time I asked for the paid up letter, I was told it would take 2-3 days… it’s been more than a week since the 2-3 days lapsed. Now they’re blue ticking me even on their WhatsApp line.