Yikes! Polyurethane over waxed hardwood floors…how do I resolve?
For how much I hate to say this (because I am a DIY’er) you should take this info back to the refinishing company and get their advice, even if you have to pay for it. If I couldn’t afford the good advice, I would get a stripping solvent and test an area of the floor. I would strip and much as I could from the floors, then get the sander. Just remember, it is much cheaper to hire this out than to replace the entire hardwood floor.