Can you confirm, as I think is likely to be the case, that the messages you are sending to all other domains other than those managed by Virgin Media (@blueyonder.co.uk, @ntlworld.com, @virginmedia.net, @virgin.com) are being delivered without error? In other words, you see this problem only with messages sent to Virgin Media accounts, correct?
I've added your issue to a long list of submissions from other businesses trying unsuccessfully to reach Virgin Media customers. You can read the very large number of reports here:
The Virgin Media response so far appears to be individual whitelisting which naturally is not doing much to solve the underlying problem which appears to be a poorly configured spam-content filtering system. If Virgin Media is doing more, I'd love to know the details. The result is that holders of Virgin Media accounts are not receiving a good deal of legitimate email sent to them and would be well-advised, given the lack of an appropriate solution from Virgin Media despite months of detailed reports, to shift to another email provider such as Google in order to quickly resolve the problem themselves.
Thank you very much, russ2204, for taking the time to update this forum. I am dismayed to hear that after more than three weeks Virgin Media has not been able to resolve your report of the inability to deliver your business' emails to Virgin Media email accounts.