Pre Sale Agreement

I have a plot of land in Andhra Pradesh, and I had an agreement to sell the land. A portion of the payment was made. This agreement lapsed at the beginning of February 2020 due to some problems with the registration process. But we have continued the deal on a verbal basis. Since Covid-19 has made travelling difficult, it wasn't possible to complete the registration even though the problem with registration was solved by the end of Feb 2020. The lockdown has been open for a month and a half, but because of the purchaser unable to get the bank to release the fund from the bank, the registration did not take place. It was important for us to recover the remaining payment to fulfil a separate deal. In the meantime, he was informed of us being approached by other parties to purchase the land. Though he did make some effort to come up with the money and be present for the registration, there did not seem to be a certain solution. Also every time we spoke on call, he would try to get the price reduced. A new party that had approached us could make the payment within our timeline for completion of the separate deal. We informed the original party, that we would be cancelling our deal with them. Now we get a call from their lawyer that we did not give them an ultimatum to make the payment. What are my options? P.s. I don't think he can make the payment and appear for the registration if we give him an ultimatum of a week.