Recurrent incorrect account emails

I placed an order for 10 boxes nitrile gloves and 5 bottles of Proguard antifungal spray in Jan 2023. Order paid for in full 23 Jan 2023. I received my order and realised I ordered the wrong size gloves so I asked if I could send back the small sizes and in return they send size large, but as I had opened one box they could send in return 9 boxes in size large and I would keep the one size small box I had ordered. The manager at the time Casey Sykes agreed and did exactly that and said there is no price alteration and no delivery charges. However after that the account team billed me for 9 boxes. I queried that in email and phoned and Casey said not to worry it was cleared as it was a simple exchange of sizes. But since then I have had several emails with bill statement that I still owe them. For me this is harassment and it’s distressing. How is it that the accounts department cannot communicate with the managing director.