We had a similar patio installed in our back yard this Spring. I would suggest they rip out your ENTIRE patio and steps and re-do completely, with the concrete gravel base. Sand should be used on top of that base (to level the pavers) and swept and tamped down in-between the pavers. The concrete gravel base should be fairly thick and installed in layers, with a machine that tamps it down in between layers making the base hard as concrete. The concrete gravel base of our patio was even extended at least a foot outside of the patio pavers and an edging was used around the patio shape with large iron "nails" pounded into that base to hold the edge shape. We now have grass growing over that extended base. Sounds like your patio and steps were not installed correctly at all.
Good luck!

I agree that they should redo the entire thing, and I would not settle for any less than that. The installation was obviously faulty, and they should either start over or give you your money back so that you can find another contractor to do the work. I would watch them like a hawk if you do let them perform the work. I wouldn't trust them as far as I could drop kick one of them.

Ther are ways to pull single paver in the midle of the job if you want to check what is under them. Generally I think you are supposed to have 10-12 inches of compacted screenigs under the pavers. Screenings are very fine crushed stone.