When you have some agreed consideration, and if you have already paid some amount (in this case Rs. 1.8 lakhs), would not be paying the balance consideration i.e. total agreed consideration LESS Rs. 1.8 lakhs?
You are an educated person, and when you have signed the agreement which says that you have not paid VAT, who will believe that you have signed it without reading?
What proof you have to say that the amount of Rs. 1.8 lakhs that you paid was towards VAT?
Again, it is more than 1.6 years.