Exactly the same thing has happened to me in the last week.
I had to leave Virgin Media when we moved house last April. I was using a ntlworld account which I was told would be closed down after 90 days. It is still alive today, although only monitored, and I can send and receive emails but cannot access Virgin Media on line to change password or delete account. Virgin Media customer services told me today that they could not help me as I am no longer a customer.
I can see that spam messages have been sent from the account as some have been returned and also the hacker has got hold of authentication codes sent from other apps which, unknowingly, still had ntlworld as my contact email e.g. Apple ID.
Welcome to our Community forums and for your first post @Causl1g
Sorry to understand that you have had an issue with an old email account. Usually these would cease after 90 days; however, if you are still accessing and sending emails, this would show as being active and as such may not be fully disconnected as it should.
I'll pop you a Private Message to take some information from you and we can get this logged to be removed and deleted for you. Please look out for a Purple Envelope and pop me a reply when you can.