Recruitment Agency - getting holiday payment

[UK345]

From March 2015 to July 2015 I had regular shifts with a recruitment agency. They phoned me about 6 weeks ago to tell me that the assignment I was working on was no longer going to them for staff. I accepted this and waited about for this particular work to start again. last week I received a p45 from them but no pay for my untaken holidays. When I started with them they said that all untaken holidays would be paid in my last pay when I leave (this did not happen). I text the agency person I deal with but they have no replied.

Where do I stand with this and am I still entitled to the money for unpaid holidays ? It's only about £50 but it's better in my pocket than theirs.