One time offer not changing in cart.

I ordered parts and waited for the "one time offer" to be displayed. I clicked it on all my items and then clicked the "view cart" link only to find it was the same price. It hadn't changed at all. I've emailed HK to ask what's going on as I haven't paid for my order but no reply email as yet. I've bought from HK for years but this is just a joke. Why have such a feature that clearly doesn't work!!!