Getting back of a sold property

Respected sir/madam This is to inform that I live in a 3 storied building constructed by my father. Presently 2 of the floors are acquired by me. The ground floor of the building was sold by my brother to an outsider in 2013. Due to weak financial condition I could not purchase the ground floor from my brother. Now the matter is the outside residing in our flat is harassing mentally 24x7 from 2017. The harassment includes such as not providing electricity bills, using common passage as garage to keep bikes, littering the passage, keeping gates open, banging doors and collapsible gates l, abusing and threatening. We informed the club of our locality but they did not take any action. We've filed a general diary against them but no good here as well. Firstly I want to know that is there any law to abide them from doing this mental harassments and secondly is there any chance of purchasing the flat from the outsider so that the building constructed by my father stays as a home and not a flat. Your opinion will be very helpful.