Builder change Referral incentive clause (from 2% to 1 %) & Delayed the referral reward amount >1 yr

I booked an under construction property in Apr 2017 via friend's reference in Thane Majiwada area. Its scheduled to complete by June 2020 (Registration, agreement all done in June 2017) Builder wrote my friend's name & apartment # on booking form & verbally agreed to pay 2% of Agreement value (1.13 cr) to my friend. They told as per their process - they pay referral after paying 20% of agreement cost which was already paid in Apr 2017 Issue 1) Builder delayed the referral incentive by > 1 year Issue 2) Builder reduced the referral incentive by 0.5% (which results to 56,000) After multiple follow-ups & email, sales team kept on delaying things... Now - they told me its 1.5% as referral incentive will be given to my friend & not 2%. There is no written document that states it was 2% or 1.5 %. Its been more than 1 year now, they haven't shared the referral amount. I got 3-4 emails, phone logs on follow-up & they have delayed the referral incentive. I've asked them to pay standard 10% interest as penalty for delaying the referral, but they are not ready for it. Total aggement cost = 1.13 cr - 2% Referral amount = 1.13 X 2% = 2.26 lacs - 1.5% referral = 1.13X1.5% = 1.69 Lacs (That's loss of 56,000) (2.26 - 1.69) Also 10% interest on delayed = 10% X 2.26 = 22,000 As builder charges 10% interest even if we delay payment by 1 day, Why can't this same rule apply on builder? Pls suggest - What should i do? What complaint should i log? Dispute in reducing 0.5% referral & interest on delaying referral incentive? regards, Sidhesh