Admissibility of unstamped agreement of allotment for consumer court

An Agreement of Allotment of a piece of land in Kolkata was made between me and the Builders/Developers on unregistered and Rs.10 non-judicial stamp paper. There is a clause in the agreement where it is mentioned that the Allotment Agreement and payments shall not be deemed as an agreement for sale. I have already made a consumer complaint in the West Bengal State Commission refereeing the clauses of the agreement for refund due to deficiency in service. The Opposite Party (i.e. Builders) in their Written Version stated that since the said agreement was prepared on an unstamped paper, the complainant can not rely upon the said agreement even for a collateral purpose. Please let me know (i) whether the said agreement is acceptable to State Commission (ii) whether the statement of the Opposite Party is valid for consumer complaint (iii) if Opposite Party's statement is valid then what will be my next course of action?