employment agency holiday entitlement

[foxyflugel]

I worked for an employment agency last year and when I left them (got a permanent post) they failed to pay me for my holiday days accrued.

I then got laid off my perm job and went back to the agency this year. It was only on enquiring about a holiday day that a young lady told me that I should of been entitled to holiday pay last year in my last wage payment. When I spoke to the boss of the agency she said: -
1- you can't have it because it is from last year!!
2 - you had to work a continuous 13 weeks before any holiday pay could be claimed - it has been changed this year and you are eligible straight away.
3 - The holiday entitlement is 20 days (inc stats) and this is worked out by the weeks worked (not including the present company's shut down week) and the average hours.

Can anyone advise if this is normal practice or if I am being shafted from a great height by this agency