Commercial college hostel is running in a residential building

I am Tarun Sharma. I purchased a flat in Udaipur (Rajasthan) in 2010 on the bank loan for investment purposes. The registry of this flat is still pending and currently no residing in this flat. The building is 9 stories high with 36 flat. 28 flats are owned by a person who owns few medical/engineering colleges nearby. Somewhere in 2013-14, this guy started a full-fledged hostel for college students in all 28 flats. The possession is still with the builder but there is absolutely no maintenance, the builder has not installed 1 of the two lifts also. There is no society formed as the guy who has 28 flats is not willing to make the society (This is what builder told us). I have been trying to sell this flat form last few years but the situation is there is a commercial hostel running in the building with all boys/girls, very very few families are residing there and there is one lift short and absolutely no maintenance in the building. So this has trashed the market value of this building. I am paying the bank loan and not able to get any value on this flat. I tried selling this to builder/college owner but they are not ready to buy it and they quoted the rate on which I bought this flat. So I am looking for a legal option assuming the commercial hostel is illegal in a residential building. Also, want advice on how not having registry will affect my prospects.