1) you are not liable to pay interest at 24 per cent as there is no clause in agreement .
2) rather builder is liable to pay you interest for delay in delivery of possession of flat by nearly 3 years
3) you can also seek recovery of rentals paid by you for flat taken on rent .
4) also seek costs for moving the consumer forum to direct builder to pay interest for delay in delivery of possession and for recovery of rentals paid by you