You have three options in such cases where builder is delaying project indefinitely. One can be to file a case before consumer forum, second can be to approach RERA and third is approaching NCLT and proceeding against the builder under the insolvency and bankruptcy code.
Now RERA is a dedicated tribunal for real estate matters when passing order it will probably either order refund of money along with interest (usually 10% of current value) or it may grant monthly interest until delivery of possession.
But consumer forum is also a good option and it usually pases an order to give possession and also grants a lumpsum compensation for delay in delivery and for mental and physical hardship suffered.
NCLT is mainly for building pressure of insolvency so that the builder offers a lucrative settlement offer.
All are good options but as I said RERA is a dedicated tribunal so it's better to approach it.
Every lawyer having experience of RERA tribunal can send a legal notice as well as explain consequences but in nutshell consequences are those as stated above.