Date wise registration and forfeit of agreement on failing to do

My mom had purchased a flat with builder during registration the builder asked us to pay 20% of total cost of our flat during registration not suspecting any foul playplaywe agreed to do so.but the registration he drafted was date wise and not slab wise we objected about it but he simply saying its a normal that theconstruction will be complete as per dates cleared our doubt. Then we kept on paying the builder as per the construction progressed.after 2 installments the construction was brought to halt and hence we stopped the payments.the reminder letter from the builder also stopped. After a year when the construction started again we payed 2 more installments and after that recieved a letter from our builder to pay our installments with interest of 14.5% on each for delay.(we never received his reminders during the halt). We refused to pay him the same.we confronted he said it was default letter and that we can pay our installment as per agreed.we suspected something fishy.yet we kept on paying the installments duly. But during possession we recieved a letter from the builder to pay a very huge amount of late interest and remainder installments to get possession. We tried to confront him but he avoided us and was andamant that we had not paid the amount and hence he has right to forfeit the amount paid within 18 days. Immediately we lodged a complaint in court.after that he also cancelled our agreement and registered our home into someone else name without informing us. My question is Is date wise agreement legal even though in allotment letter he made slab wise agreement. And what else charges we can catch him on And will we get our home back or replacement home or a compensation in this conditions. Please help