Paid up letters and Refunds

I had two Standard bank Credit Card which I have paid them in April 2021, After paying I also made some payments as I was given a settlement amount. They are do not want to give my credit refunds and paid up letters. I spoke to their agents who confirms that accounts are paid up and will escalate the matter for letters and refunds to their Manager who is (Percy) I also sent email to Percy their manager and Arthur Monchu with proof of payments neither of them responds to my email and whatsapp. Kindly assist as I have paid them and now they do not want to give me my refunds and paid up letters. Thanks