Aliens Developers Private Limited - Builder not returning money after cancellation of booking

Booked a *BHK flat in "Aliens Space Station Tellapur Hyderabad" on July ****. I was told possession date will be Jan-**** + * months grace period. I have paid **% of total flat cost as booking amount and remaining amount was decided to pay with home loan. But later I came to know project is delayed since **** and I also didn't see any progress of station * in which I have booked the flat. So I requested for cancellation in March ****. Their cancellation team prepared a DOC stating that amount will be refunded back in instalments without any interest and first instalment will be in May ****. But now its Sep and I haven't received a single rupee from the builder. Every time I contact them, I am getting assurance that its already in process. The person from cancellation team is now not answering my call. I am very tensed now. Did number of trip to their office which is **km from my current location but every time I ended with wrong promises. They are not bothered about customers and there are already so many cases against them. Please help.
Attaching first payment receipt. I can share all other receipts or other deed document if required.