Overdue payment?

We received a bill for an overdue payment but this doesn’t make sense because a. We have asked for the account to be closed, b. My partner called last month to settle any back payments, c. We have direct debit and so any payments still owed should be taken from the account on file. 
we have called the virgin number and the automated service did not recognize our account number for us to try and understand the reason for the bill. 
please help. Who can we talk to and how?