Having installed as per guide I expected 1 year free subscription but instead got only free trial which has now expired
Sorry for my reply. I am only an F-Secure user (their home solutions).
One option is try to contact their official F-Secure Support Channels (chat or phone):
Just as ability to check your account and subscription information.
Another option is own try to doublecheck that your registered account is pinned to Virgin Media promotional (and that promotional is still active/valid).
For example, when you login into your F-Secure account - does it branded by Virgin Media logo?
If not - probably account is not pinned to noted offer; and maybe possible to re-try and to register account with provided steps (with doublecheck that all required information like cookie, specific exact URL and other points are there).