Thunderbird is the postman, it goes off to the sorting office, gets a copy of your post and brings it to you.
So, as others have said, under tools, accounts, server settings make sure it goes to the right shelf in the right sorting office. The virgin media help pages will have a how to page for pop3 or imap, it's quite likely your turnpike settings have got mangled.
But first you can go look at the sorting office yourself and see what's there using webmail. Webmail doesn't bring it to your machine it just let's you look at it, I use it a lot when I am travelling because you can use it from laptop, phone, ipad, someone else's computer.
Again, virgin media help pages will tell you the webmail settings and you can use your normal browser ( chrome, Edge, whatever) to go look. Virgin might not have the facility but I would be surprised if not.
No need to make changes to your email, just get the postman (turnpike edit, thunderbird) doing the job properly.
I would use webmail to see if anything is there, then try and fix turnpike. Edit tbirf
One thing that can mess up collection is time and date on your pc. Normally that's set automatically but if it's wrong the mail server (sorting office) can't work out when you last came.
Another thing might be a full mailbox. If turnpike tbird never deletes email from the sorting office, virgin might be rejecting incoming because the box is full. Send an email to yourself and see what happens.
I've used thunderbird for years to collect from various sources and had very few problems.
