Seller not refunding the Amount

I entered in a MOU(On 100 Rs. Stamp paper) for purchase of an under construction flat with a seller. Seller has signed a Registered sale agreement with Builder but does not have sale deed executed in favor of him. Seller took me to office of the Builder where Builder's representative confirmed that property can be transferred on my name through assignment agreement executed between me and the seller and Builder will also sign that as consenting witness and at the time of possession builder will execute the sale deed in my favor. I paid seller token advance of Rs 5 Lakh and on date of signing MOU I further paid him Rs. 13 Lakh. I also paid stamp duty for assignment agreement to Builder's manager and assignment form along with my KYC details and Post dated cheques were submitted at Builder's office on date of signing of MOU. For payment of further amount following terms and conditions are mentioned in MO " i)Rs.xxxxxx will be paid by the purchaser to Seller on signing the Assignment Agreement. ii)Rs. xxxx will be paid by the Buyer to Seller through Bank transfer/Cash//Bank Loan after completion of the assignment agreement. iii)Rs.xxxxx will be paid by the purchaser to Builder according to the payment schedule. If the Purchasers are unable to pay the amount given within a period of 45 days extendable to 90 days from the date of signing the MOU, this MOU will become null and void and any further amounts paid will be refunded to him by the Sellers after deducting Rs.5,00,000/- (Rupees Five Lakhs only) towards liquidated damages, without any interest on the advance. The First Party can enforce this MOU for specific performance. Similarly, if the Sellers within a period of 45 days extendable to 90 days from the date of signing the MOU can be enforced for specific performance of contract by the Purchasers. He shall also pay of Rs.5,00,000/- (Rupees Five Lakhs only) towards liquidated damages to the Purchasers." Although 90 days period for payment was agreed the seller started demanding the payment from 28th day onwards citing the reason that he has signed assignment agreement on 13th day after signing MOU. The seller signed an undated assignment agreement and sent it to our home address for signing on 15th day after signing MOU. He did not demand the money then and asked us to sign and send the agreement it to Builder for completion of formalities at Builder's end. I signed on that undated assignment agreement and then sent it to Builder. Seller is not allowing me 90 days time to arrange the funds and pay him. He is asking me that he will refund the amount which i have paid to him If I will to sign the cancellation deed. Please suggest if I can take him to court for payment of liquidated damages as he is cancelling the deal within 90 days and is not ready to refund the amount also.