Should my orthodontist charge me for Invisalign refinements?

Hi, I've been with Invisalign for a few months and currently on tray 15 (out of 24). Unfortunately the upper tray doesn't fit perfectly anymore (a few large gaps between tooth and aligner) and my doctor recommended getting refinements in the middle of treatment now. He wants to charge $500 even though he promised me at the beginning of treatment that there were no addition costs. I guess he meant it for the retainer though I'm quite sure he mentioned refinements as well but no way to proof.