sounds like you are correct. With all you have tried, you might need to seek professional guidance on further cleaning off the haze. Then if nothing works after this long, then contact the builder or the installer and voice your discontent.
After the grouting, many cleaning of fresh water is required to clean off the grout haze and residue. Sometimes 10 fresh water washings especially over darker colors.
What you have already done should have resulted in some improvements, but since they have not, I would say the residue has cured out and there to stay.