No help from customer service at Jet.

I phoned Jet in October to get a settlement amount as I wanted to close my account. The gentleman gave me the amount and told me my account would be closed as soon as I paid. I settled the amount on the 30th of October 2020. I get daily calls now informing me of an amount due for interest and club fees. I have phoned and emailed at least six times telling them that my account is closed. They have no proof of my payment on their records (so where did my money go?) I have sent them proof of payment four times and get the same answer every time. "get a printout from the bank itself" Why is my proof of payment not good enough? I have had this account for 27 years.