Hi Mark - thank you for the reply.
I hadn't rung the number because I thought to see if I got email notification of billing on 18th as usual, and whether I did or not, then phone and ask.
What I was really wanting was confirmation in writing that my account was fully paid and now closed.
However, I just tried logging into my account and it appears to have been closed. So, I rang the number you gave - this is the same number I requested my MAC code on, but this time I was not speaking to someone in the UK.
I was told not to close my DD yet and to see if I get billing notification on 18th and then call them back after that date to request a manual refund on any amount due back to me (probably the full month).
So, I'll do that and also ask for written confirmation that the account is finalised.
Hopefully all can then be concluded smoothly and the DD cancelled

To be honest, a refund was the furthest thing from my mind and all I wanted was to be able to cancel the DD knowing all was in order.