Cancellation of a Plot

I had invested in a 264 Sq Yard Plot Commercial plot in August 2007 and till December 2009 i have paid 46 lakhs to the Developer. The total amount agreed was 54 Lakhs + 5 lakhs for EDC charges. After that the developer did not send any demand for 12 years Now Suddenly i have received a letter by Registered post from them cancelling the plot Claiming that they have sent 2 demand letters in 2010 and 2011 and as i have not responded for 10 years - they are cancelling the plot and they will refund my amount after charges me all the costs and consequences pertaining to cancellation I have not received any demand letter from them. Please advise whether they are justified to proceed in this matter and how should i proceed in this matter