protect the rights

sir
i entered into an agreement to buy a flat at hooghly district (WB) when building in/outside pluster was completed.
Afterthat developer provided me a Sale Deed when i wanted to get registered my flat. Registration is yet to done.
I found a different in built-up area. The difference is as follows -

As per agreement -
Total area 1070 sqft
(Carpet 751+built-up 14%+superbuilt 25%)

As per Sale Deed -
Total area 1192 sqft
Carpet 751+built-up 27%+superbuilt 25%,)

Developer increased in the sale deed the built-up area from 14% to 27% i.e. 13% hike which is beyond the agreement.

Kindly advise me : 

1) whether i should make the payment as per inflated sale deed including hike of built up 13% or made payment as per agreement signed. 

2) who is the appropriate authority/rule to appeal for protect my rights.

Awaiting an advice to save my loss.
Regards,
Rk Ghosh