Receiving calls from collection department when the account is settled and received refunds. **** COMPANY

This is about the 3rd time i am complaining about this company. I settled my account with them on the 8th of Dec 2021. when i checked my account online they has zero balance showing they are closed hence on the 20th they continue to debit my account. Fine i logged an endless query for my refund which they eventually paid on the 28th Dec 2021. To my surprise 2 days later i am receiving calls from their collection department claiming that my account is in arrears. How can i be refunded and hence you continue to say the account is in arrears. What utter ******* is this. Please close my account as i have fully settled you.