Which department in this government proves me that this property is legal to buy?

Respected Sir/Madam, Very Good Morning! I have trusted a Sales Manager who recently became friend and booked a Flat in Apartment (BANGALORE) where he is marketing one of their projects. I paid blindly 15% of amount of the Flat by trusting as he said everything is legal. After suggestion from few of my friends, who scolded me and asked for a Legal Verification, I took legal docs from the sales manager and gave it to a known Lawyer to verify them if everything is fine. The lawyer’s opinion on property shocked me that this is not a good property and illegal based on following points attached to legal documents. 1. This property was a granted land by government for SC/ST which cannot be bought even after 1000 generations because as per Indian Law they can take this property back at any time without any compensation to the purchaser / multiple purchasers 2. PTCL Provided by Government is Temporary but not a permanent solution and may have issues in future. 3. Court Order Copy provided by Legal officer on behalf of Builder/owner of property with Judgement in year 1996 is not a permanent solution and may have legal issues in future. Lawyer stated that it clearly shows that SC/ST People who sold their land in year 1968 and after the Amendment act came into LAW in 1978, the same SC/ST people have approached court immediately in year 1979 saying that they are the real owners of the property which court has passed the judgement that this act is not applicable due to SC/ST people sold it before the 1978 Amendment act came into LAW. The present purchased owners and SC/ST people have to bear their own costs and 1978 ACT is not applicable to this property. I am a middle class person at age of 40 and this is my first property that I am buying after pooling my money for six years and gave whole money (15%) of the property cost. 1. I am fine to purchase this property if it’s legal; else I want to cancel the agreement. 2. Builder has mentioned that he is going to take/charge 10% of Total cost of flat if I am planning to cancel the agreement which I will be losing my hard earned six years money. 3. Which department in this government proves me that this property is legal to buy? 4. What is the solution to get my money back if I cancel the agreement? ================= Mistakes done by me ================= 1. Trusting a new person foolishly and making an agreement of buying the flat directly 2. Paying amount to buy without a legal advice 3. Spending sleepless nights with tension thinking how to get my money back I request a genuine Lawyer to respond back on this. I am fine to provide the legal docs provided by builder. With Best Regards Kumar