froude case in flat saling

Dear Sir, I really in a big problem. i booked a flat before 2 year @ 2150 per Sqr feet just beginning of the construction. the broker of that flat told me he was the promoter of that flat and shown me a 650 sqr feed flat I paid 20% amount on flat at that time and did a agreement with stamp paper but after 50% of completed the construction i found that that flat was defected and have some problem so i asked that broker to change this flat and give use another one (850 srq feet)on 2nd floor and told me ok no problem all the flat are not booked yet so we can change your paper and provide you in second floor at the same rate( 2150/ sqr feet) and new agreement paper will provide you as soon as possible . again he asked some money for that flat and told me i will handover the new flat agreement within 2 days and i paid rest of the down payment amount . from 6 month I am asking for my new flat agreement ( changed one) but he told me every time give you today/ tomorrow and all the excuses finally i go to that flat and ask a person that where is the broker he told me that i am the promoter of this flat and I did not received any amount from that broker and now i am going to sale this flat to another person if you are interested then pay 2500 per sqr feet. sir i cant explain that how could i manage that amount because and cant pay that higher amount so please help me.