I agree with the suggestions of other learned professionals Your contract with the builder and your loan contract with the bank, are two independent transactions. Your liability to clear the bank loan by prompt payment of EMIs continues notwithstanding the possession or otherwise of the flat.
You have not stated the relevant fact whether upon your visit to the construction spot (which is necessary for your evidence in court), whether you found the flat constructed and if so what all work including amenities and approach roads, drainage system, fire safety etc. remain to be done. Also another relevant fact omitted is whether there is time overrun as per your agreement with the builder and if so to what extent.
It appears you are also a victim to the current culture of reliance of 'talk over phone, discussion,meeting in person' and the like. What is important is good old pen and paper.
1.Inspect the premises, carefully note down on PAPER (not laptop) the stage of construction and all relevant shortfall in work as per agreement, in fullest detail.
2. check the notice clause in the agreement whether notice is to be sent by registered post acknowledgement due or a email communication is permitted.
3. send notice in writing mentioning all deficiencies by post or email as the case may be (not through courier) and calling upon the builder to complete the construction with all listed amenities and hand over possession within 30 days of receipt of notice.
4.carefully preserve copy of the notice, registered post receipt and acknowledgement card in a file, alonwith the agreement. (if ack. card is not received within 15 days write to the post office, wgho will provide a certificate of delivery).
5.check whether there is arbitration clause in the agreement and evaluate the same in the light of recent amendment to the arbitration Act 1996, with legal assistance.
6.File Consumer case,upon advice received, and pursue the same to its end diligently, with legal assistance.
7. Inform the bank, with a copy of the notice and also the consumer complaint details in due time. But no relief woul;d be forthcoming from the bank. Request the bank head office to blacklist the builder, which they may,in their discretion act upon.
8.Be prompt in payment of emis to avoid problems with the bank.