Update as of 22/06.
I got through to someone and my original fraud case had been closed without me being notified. Virgin Mobile have continued to attempt to take money every month and I now have multiple missed payments and a default/repossession on my credit report.
I raised a new query and a new fraud case was opened. I was informed that I would receive some form of confirmation with 72 hours and nothing has come through.
Here's the timeline for anyone who is interested;
8th of October 2019 - initial contact
16th of Feb 2020 - try the (useless) SMS system and end up having to call. Fraud query raised
27th of March - 51 minute phone call. Nothing useful.
3rd of April - 1 hour 31 minute phone call.
16th June - most recent call.