Yongzhi Ong

Hi bro and sis, I recently engaged a contractor to overlay my kitchen flooring. Required them to repair some of the old tiles with air pocket. What I notice was that, they have applied water proofing with all the old tiles still intact. When I asked if they have repaired the tiles with air pocket, I was told that, what they did was to "remove the tile, apply cement and stick back the tile". So all the old tiles will look in tact even after the repair work was done. Does such method exist? I am quite skeptical about it and have some worries that they have not done the job and billed me for the repair work. Loo forward to hear some advice. Thanks!