Consumer Protection Act (68 of 1986) , S.2(1)(g), S.12, S.21— Deficiency in services - Delay in handing over possession of flat by builder - Claim of interest by purchaser - Delay occurred due to orders passed by National Green Tribunal - Agreement for delivery of possession providing for grace period of 6 months - Failure of purchaser to take possession in time in spite of builder obtaining completion certificate - Purchaser entitled to grant of interest after expiry of grace period till obtaining of occupancy certificate. (Para 4 5)