Ongoing calls, emails and smses on closed Acc

This is by far the worst company to collect for clients, I had a foschini acc of which I settled on the 13 march 2021 via a D/O and I was told I can't get any discount so I paid the entire amount, to my surprise today I get a call from them and claiming that I owe even though they can see the account was settled.... When asking for clarify on the matter, I was advised that they will escalate the matter, yet they called me religiously since the payment was done and told me to wait for the PUL within 14 working day . I will not be paying anything as I've settled my account and I expect zero nonsense from CSS concerning this matter.