1. builder is right
2. he is only going as per the contract
3. if there was any issue from the bank's side in disbursing the amount, then the purchaser was liable to make the payment to the builder before it became due
4. when bank sends a disbursement, it gives a message to the customer that so and so amount has been paid to builder towards EMI
5. if there was some issue with the bank and the amount was not paid on time, then you should have paid it. When you did not get message from bank about the monthly EMI payment then you should have inquired with the bank and intimated the builder immediately and also requested the bank to send a message to the builder clarifying on the point
6. so i do not see the builder at fault here
7. now since the payments were missed and due to that you have to incur interest payment, then your remedy is against the bank and not the builder
8. the bank ought to have notified you promptly about the glitch. Since it did not do that (i assume) the bank is liable for deficiency of service
9. so please claim the interest amount from the bank by writing to the banking ombudsman
10. simultaneously you can also pursue matter with builder and request him to waive the interest due to the peculiar circumstances