When I got my Virgin Mobile (UK) Sim a few months ago I found that it
had some problems connecting to a few numbers, so I naturally decided
to contact the company and get it fixed. My conversations with them
are too long to post here, so I've just put a link...
http://www.seabhcan.com/dearvirginmobile.html
I'll just say that after several weeks of e-mails and phone calls,
having never spoken to the same person twice, and after never having
the problem fixed, I switched to o2.
They are also dire, but at least it works most of the time.
Mark.