Glad to hear your phone issue is now sorted. I think the best option for us here is to try an alternate Virgin sim. Give us a call on 789 or 0345 6000 789 and we'll sort this out for you as soon as possible.
Sorry again for the inconvenience this issue is causing, I've been speaking with a member of our team about a solution to this problem and I'd really like to locate your account to request it's looked it in more detail.
To allow me to do that, could you respond to the private message I've sent with the requested information? You can view the message by clicking the purple envelope on the top right of this page.
As you have just discovered truly faulty SIM cards are very rare, dirty contacts or incorrect seating/positioning are much more likely.
Your Virgin SIM works in ANOther handset. An O2 SIM works in your LG. So likely your Virgin SIM is fine.
Hence I am wondering if the LG is set to 4G/LTE only. Virgin Mobile does not support 4G/LTE modes. Only 2.5G & 3G modes are supported. So look in the settings and see if you need to enable or switch on 3G. Switch off 4G/LTE or 4G/LTE preferred and then power off the handset and then power it on again and see what happens.
For Android Marshmallow this setting is found in Settings>Wireless & networks>More>Mobile networks>Preferred network type