I've removed your other post because it was a duplicate.
That is definitely not Virgin Media's official complaints site; no ISP has a website just for complaints. The complaints procedure is started internally when you action a complaint and if after 8 weeks you fail to reach a resolution then you can request a DEADLOCK letter from your ISP and pursue it through an ADR scheme.
Full details can be found in this section:
http://www.ispreview.co.uk/new/complain/complain.shtml
Virgin's complaints handler ADR is CISAS.