Just put my new sim card in the phone and it wants a network unlock code.
The bit of paper with the new sim suggests I visit virginmedia.com/unlock to check the number. virginmedia.com/unlock says no such page? Having a look on the site it looks like you need this code when changing network? This phone has always worked with virgin.
I gave up on the contact/help pages as they take me in a circle of contact us through something like message us and it doesn't give me a clue how to do that.
I am not much of a phone user as you may have guessed. I just had a code to verify a login texted to me and the phone doesn't want to work.
I don't know what you found unless the page was down when you tried it (wouldn't be the first time a site has a page go down temp), but I googled the phrase you used, and it was the 1st result (But, never touch the first options that have Ad by them), they are simply adware, it's not malicious, but I always avoid it as too much can slow your system down, anyway the link I found is;
That said, I don't think you need it, the following link explains lots about this, and simply says every new sim needs to input 7890 the first time, it could be as simple as that, really annoying when you have looked for deeper issues, but try the code I just gave, then have a look at the following link to find lots of info about this, hope it helps.
My brain woke up (sorry I nearly died before Xmas so not on top form), there is a serious warning with mobile codes, read the last link before anything, because if you try, or have tried to enter a code more than 3 times incorrectly, Stop, the 4th wrong entry will lock the phone needing a PUK code, you can get those within your account if that happens, but do Not guess it, you need to contact Virgin (it's the last bit of info), it looks like they are proactively putting security on your phone sim, so it is wise to change that as soon as you can, because you will need to enter it every time it powers on after the battery has gone flat, or you had simply powered it off due to being in a meeting or similar, so read the last link, it lists the points that r4elate to this.