How can I get my payment refund from builder legally.

In 2016 to till date I have paid 18lacs to the builder which is 90% of the value of flat I bought and It has been 2 years since there is no progress in the construction of the building as the builder has stoped all the construction and I paid the amount in installments to the builder when the foundation of building was laid and now when I ask the builder about the completion date of the builder He refuses to give the possession of the flat and also denies to refund back the payment. Also, there was no agreement of sale or allotment letter given by the builder even after being asked to hin several times. The builder was known to us and we trusted him but later we also came to know that the township and building he is constructing is not registered under RERA. kindly let me know what legal action can be taken against him under RERA and other than RERA too because it has been 2 years since there is no progress and I want my money back as per the current rate of the flat that I bought and started paying for 4 years back.