Beware of Owner's share apartment in this building

Q: Planning to buy an apartment in this building. Beware of the flat no: 002, 301, 302, 303, 304, 305, 405. All these belong to owners share. I was also interested in this building and made 20% payment for 302, went in to sale agreement with the land lady. But now she is refusing to honor the sale agreement and refusing to register the flat stating that there has been delay in the payment. The sale agreement was done on 1'st of Feb and i had applied for loan after that. The lawyer for legal opinion had demanded for certified EC which was furnished by her employee on 1'st of April. After the legal and valuation, the bank had sanctioned the loan on 11'th April, but now she is refusing to register the flat and is saying that if you need the flat pay more or the deal is cancelled.