You are having information. You have tried through proper authorities. Authorities are negligent. Get suitable order from court both against the authority and to the owner as expeditiously as possible, if owner has not applied for such regularisation scheme so far.
You can also file application to Public Information officer under RTI Act as per format and fees prescribed for RTI in their website and get the information that supports your further action.
Brief Facts: Unauthorised construction at.....................by.................... My complaint dt......................
1)Please inform action taken on my complaint with day to day developments as office notes.
2)Please inform specific reasons for keeping silence on such unauthorised constructions which amounts to encouragement.
3.Plese inform further steps that can be taken as per law by the authorities.
4.Please inform the name of the superior officer, designation, mobile no, and address with whom a complaint can be made for inaction of lower levels.
5.Please inform the name of the Inspector/officer that failed to notice such initial stages of stopping the construction, with full knowledge that such activity is unauthorised, and the action authorities are going to take against him for his negligene.
6.Please provide list of identified illegal constructions as per your records and action taken by authorities so far.