When/if you set up a Direct Debit, you should have received an email from firstname.lastname@example.org with a copy of the Direct Debit instruction attached. Within this document, towards the bottom you'll see two references (a Service User Number and Reference). The Credit Agreement Number is the 9 digit Reference number.
I don't work for Virgin Media, so I'm afraid I can't resend it. You'll have to ask them to do that. Alternatively, you could check with your bank. WIth my bank app, I can see the reference associated with the direct debit.
Calm down. This is a community forum. I don't work for Virgin Media. I was just trying to help. For me the security PIN *IS* the last four digits of my bank account, and has been on every occasion I have upgraded my handset.