Refusal to refund me my money

This bank has a tendency of loving to be an outcast. I accidentally overpaid my loan account from credit card after it was settled. Now I called them on Tuesday asking them to do a transfer to my world account, the lady told me it's possible however we had issues with authentication due to network issues. Today, I called again and this lady is telling me that she wants a proof of payment from the account that settled that loan. I want a refund of the money I paid, why would you demand me other things? And I'm saying transfer it to my world account, yoh the nuisance of the lady is refusing to understand my point. So keep that money African bank, make sure it yields interest, I will come back to claim it after 10 years. I have no time for outrageous demands. I know my consumer rights. I want that account closed and reflecting as such on credit bureau. Don't make your problems my problem.