Cancellation of Allotment of Flat

The original buyer Mr.ABC booked flat by paying booking amount 12,30,000/-(cash + cheque) and 22,00,000/- in cash in between 2011 and 2013 and got allotment letter.The total agreement value mentioned in the allotment letter is 48,75,000/-. In 2013, because of financial difficulties decided to sell the flat.He offered me to purchase it.We have executed a MOU on 100/- stamp paper in presence of 2 witnesses. I paid all the amount which Mr.ABC has paid to builder and on receiving the entire amount the builder issued NOC to original buyer Mr.ABC and transferred the flat in my Name in 2013 after receiving additional 12,30,000/- in cheque mode from my account..But Agreement for sale was not executed between original buyer Mr.ABC and the builder. Nor did the builder was ready to execute agreement with me. I kept on writing emails and letters, but builder was not ready. Now the builder received Commencement certificate on 26 April 2019.He sent me notices to pay additional 13 lakhs ( which he says is as per the RERA Payment schedule) and complete the agreement and Registration process but not for the allotted flat but for some other flat for which he was asking me to pay 4 lakhs extra as floor rise. As per him the allotted flat due to technical reasons does not exist and he by his choice selected a flat on some other floor.I was adamant for any change in the flat. i also paid the stamp duty of 4,65,000/- as per the market value of flat.Now again the builder has sent me notice that since i did not comply with the rules and did not pay 13 lakhs he has cancelled my allotment. Also he has said that he has refunded 12,30,000/- to the original buyer Mr.ABC in cheque mode in 2013 itself. Builder is not ready to speak anything about the cash which he has received in cash from original buyer Mr.ABC. As per builder whatever he has received from original buyer Mr.ABC he has refunded back. Further he will refund only the amount paid by me through cheque (12,30,000/-) that to after deducting 10%.The original buyer Mr.ABC has taken money both from me and also from the builder thus reducing my part payment consideration.Even after paying 46,60,000/- as well as the stamp duty of 4,65,000/- builder has cancelled my allotment. The original buyer Mr.ABC has not yet handed over the payment receipts of the amount he has paid to the builder inspite of several requests. Shall i approach RERA or file a consumer case against builder. Also a civil and criminal case against The original buyer Mr.ABC.