Well, I spoke online to the support team, The sim was not activated (the letter it came in did not state this, Nor did it state anything about a switchover, It just said pop it in the phone and wait 10 mins)
So the sim was activated. And apparently my phone is locked because it didn't work even after that.
I went online to find an unlocking service. Of the 6 different ones I tried, None of them could unlock the device.
So I have had to buy a new secondhand phone. Still waiting for it's delivery. So I am still without a phone.
I am not happy with the way virgin has handled this at all. No one mentioned a thing about networks being changed, Either in the letter or even when I spoke to support and they activated the sim.