Ownership Right in land

I had purchased one second Floor Flat in 240 sq.yd plot constructed G+3 stories in year 2003 with registered sale deed mentioning proportionate undivided & impartable ownership rights in land underneath.The remaining three flats in building belongs to original owner of building . Now owner has sold all three flats to one builder with ownership right to dig basement in 240 sq.yd through registered sale deed. I have a collaboration agreement with builder that he will give me my second floor duly constructed without any cost with car parking and lift . Now builder has demolished all building and constructed basement ,Stilt parking and G+3 stories building at his own cost. While asking him to give our 25% share in basement ,he refused and told that he has purchased right to construct basement from owner of ground floor. Kindly tell me whether I am entitle to get my 25% share in land or not and also let me know that legal case to be filled on earlier original owner or builder who purchased the right to construct basement. Also clear whether I am entitle my share in basement or not.