Cancel Joint Venture Development Agreement since no Progress

I am a law student graduated out of college this year and came across an incident which expected my opinion for legal proceedings. Request all your Support and advice to handle this issue. There is a Joint Development Agreement signed between 2 parties during 2010 and there was no activity performed so far in the piece of land by the developer. The Developer has given 10 lakhs advance which is stated as Interest free money in the Agreement. The owner has waiting 5 years and does not want to proceed further with the Developer since there is no confidence that any project would kick start in the near future by the developer. The land owner wants to cancel the agreement and refund 10 lakhs and explore other options but the developer now demands 70 lakhs as compensation by calculating 3% compounding interest for the past 5 years. The Agreement has a grace period mentioned which states that if the project is not completed in the next 36 months the developer should pay 5 rs/sq ft to the land owner. During discussions between the Owner and Developer it looks like the Developer is very rude and does not refer to the terms mentioned in the agreement but just keeps asking for 70 lakhs to hand over the documents and cancel the agreement. The demand of 70 lakhs was communicated to the owner in a mail which had an Excel sheet attached with calculations. Original Land documents were collected by the Developer and handed over to a third party few months back stating that the concerned firm will work in getting the necessary approvals. The Joint Venture Development Document is an unregistered agreement between both parties. Please advice the best possible ways to handle this dispute.