Closed cheq account in 2019

I have been receiving calls from NDS calling on behalf of standard bank for a cheque account that was closed in 2018/2019, NDS is saying l owe standard bank, however there has not been any statements, calls emails from standard about an amount owing on the account.Todate l have been told over the phone that l owe and nothing has been produced in writting as to what exactly do l owe. I went to the Sunninghill branch they said the account is closed however they will escalate this to the manager the next day, as the manager was on sick leave and l will receive a call the next day, its been a month and no call. The call centre also says the account is closed. So why are your attorneys calling me.