This appear to be one of those dodgy rip-off companies offering "prizes" of holidays:
http://www.whoopydoo.net/The only contact on their website is by e-mail. Have you tried that?
The only reference to the number you gave (with either 0845 or 0844) is on the "Phonespamfilter" site, which says it all really.
The domain name whois gives the address:
Fireball Media limited
The Grange
1 Hoole Road
Chester, CH2 3NQ
No phone number. But you could write (by recorded delivery, if you're having problems with them).
If you have been offered a "free" holiday but have yet to contact them about it, I'd suggest you don't. There's no such thing as a free lunch, as they say. Far from being free, it'll cost you a lot of money, and I really can't understand why this sort of thing hasn't been clamped down on.