Hi Deepa,
That is a lot of payment without signing the sale agreement. Normally, only a token advance is paid before signing the sale agreement and then the rest of the amount is paid. I understand that this was done to limit the charges but there could be a thousand reasons that the builder might cite to increase sale price.
I would suggest that all the affected owners form a group. You could form a group using one of the social platforms available or through our
group management facility which can be set to private mode.
Once you have formed a group, you could approach a lawyer and through him approach the district consumer forum, which is quick and inexpensive to resolve such consumer issues. I hope that some of the members are not NRIs and are actually present in Mumbai.
Thanks and regards,
Krish