Exactly the same has happened to me. I managed to speak to an advisor this morning who was polite and initially helpful, but when he transferred me to someone 'who could help' the connection was cut.
I suspect the problem (code rejection) is because it is for an old keypad phone, but for a large company making big buck profits this is totally unacceptable. I think the worst thing is the difficulty in contacting any form of useful support; I'm sick of being sent round in circles and am ready to leave VM.
I later googled reviews for Virginmobile and surprise surprise: 1/5 stars!
Same problem. My phone is an old simple one and the keys were not registering with new sim - just showing an asterisk. And I was asked for a network code? Which I don't have? And no helper has told me the network code or why this is happening.
I put my old sim back and the keys now register but when I try to send a message it says 'error' or phone - it says emergency only.
My phone was functioning fine before. Will never use Virgin for anything again.