In residential apartment some one can register of shop from paying more stamp duty

in my building where I live is of G+2 Floors and in the road side the power of attorney holder had sale the flat by converting shop by paying more stamp duty but the builder has build as residing apartment and the shop owner is treepass the space of parking and at present they are using as the flat and they pick up the door on another side and they are paying the tax to municipality of flat what is the solution