Holiday Pay

First time contractor here. I'm about to sign an inside IR35 contract under an umbrella and something sounds fishy.

A portion of my rate goes out to "Holiday Pay" and the contract says I'm entitled to 28 days holiday days as per UK regulation. However, the umbrella company is telling me that when I request a holiday day, I will not get paid for it. Sounds really bizarre since I'm paying for the holidays, but I'm not getting paid for them. The umbrella company says this is standard and all inside IR35 contractors in the UK work like this. Is this normal?

Thanks in advance!