Advance Paid but Agreement of Sale not siged yet

We invested in a property in Hyderabad by paying the token money against which we received a receipt with no revenue stamp. We were asked to pay the first installment within 2-3 months of token deposit and was informed that agreement of sale will be signed at that time. First installment was also paid within due time and against this also we received a receipt without revenue stamp. All the transactions were legit and account transferred (no cash payments). Now, its been months chasing the builder to share the agreement but they are delaying it by saying that we will receive it next week or in couple of weeks or so. Most of the communication done so far has been on phone or in person. We have couple of mails from builder in above context where they have confirmed receipt of payment and stated that agreement will be signed in 10 odd days which was months back. What can be done here legally? Reason of investment was to save some capital gain tax. So i am not sure if cancellation will affect me there as well. Please guide.