Whilst your original post conveys your frustration, it doesn't really provide us with anything useful.
See my post here for some advice on how best to get the help you need when posting.
With that out of the way let me ask you a few questions.
What happens when you send via Thunderbird, do you get any error messages - if so please post them.
What are your current outgoing email settings?
What error messages are you getting from Webmail?
Have you tried clearing your cache and cookies?
Finally Solobo's advice is sound. Continuing to use your ISP email address as your main address ties you down to Virgin media. You may say, as many do, but I have used this for years. Let me make this analogy.
If you've lived in the same house address for years but want to move, would you -
Move house and notify people of your new contact details.
Stay at the same address, because everyone knows it.
I would imagine the answer is 1. Think of email the same way. You can monitor the ISP email to pick up anyone you may not have notified but ultimately once you've moved to a dedicated email provider, you're much less likely to encounter issues such as this.
Only use Helpful answer if your problems been solved.