When you say "on my TV but not Virgin", I presume you mean that your TV has a Netflix app which works for 4K but you're only getting (again, I'm presuming) HD via your VM TV box?
If so - can you confirm you definitely have a V6 and not a TiVo? Check here if you're not sure. Asking because the TiVo doesn't support 4K, only the V6 does.
What settings have you changed on your VM box?
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks