Work place holiday entitlement?

Got 8 days holiday to be used before the end of march and been going to my boss and hr with requests since october
and all have been refused due to to many other people off those weeks with is fair enough. So i just said allocate me whatever is free
as im not fussed when just want what im owed. Anyway spoke to them today asking what they've sorted for me and basically been told
i've lost the holiday as all weeks/time now fully booked??? can they do this? Also they wont pay me for it or let me carry it over?
So where do i stand? Thanks