Dear Mary
You are lucky they halted the job, before going ahead and creating a poor installation. I've heard too many horror stories about humpy subfloors. They would have blamed in on your house condition.
But to answer your question, no, you should not try the quick fix of pouring lightweight concrete on the particle board, it will be cracked up in no time. Simply hire a carpenter to remove all the particle board, sister the joists, if they are out of level, and install new 3/4" plywood subfloor. Or upon removal of the particle board, you find another layer of old subfloor shim it level and install a thinner 1/2" plywood. Either case it's a floor carpentry job, that is out the expertise of these installers. You can then have a glued or nailed down hardwood floor installed.
I don't know why your hardwood floor supplier did not tell you all this before you bought the wood. You may consider this all too expensive and may now want to return the wood, which should be an option.
