Non construction of property

Sir, need your valuable advice on a property booked by me in June 2014, hence possession promised is in 2017 June. But after taking payment till 3rd slab in June 2016 builder has stopped the construction work or has slowed down extremely with only 10 workers on the site. On discussing with the builder he says construction is going on or says you can apply for refund which might be returned only after 8-9 months in 2-3 successive instalments that too without interest. Kindly help what should be the next step from my side. i) should i wait for the completion of the project which doesn't seems to happen as per the time given for possession. ii) should i go for refund process where i don't know he will refund it or not or might not give after giving first instalment. A doubt as coming up in my mind. ii) should i go in for the case to get the refund which may also take lot of time. I am completely in a state of dilemma. Please help to take the correct stop so as to ensure i don't suffer a loss. Thanks .