Payable amount was to be decide including GST and same would have disbursed through bank loan, now separate demand is not valid and will be only 5% if no input tax credit. Complain to RERA for any illegal demand.

1. if the builder has availed benefit of ITC then he has to pass on the benefit of the same to the flat buyer by way of reduction in the consideration 

2. if the builder refuses to pass on the ITC benefit then it amounts to profiteering against which you can complain to the national anti profiteering authority at Delhi [check their website]

3. the complaint can be submitted online on paying some nominal fee online

4. you can make the payment 'under protest' as of now to the builder so that you do not breach the payment clause in your agreement

5. you can also lodge a RERA complaint against the builder to exert pressure on builder since he is indulging in unfair trade practice [section 7 RERA] by not passing on the ITC benefit 

6. under the State and Central GST Acts, under section 171 of the same if i am not mistaken, the builder is bound to give ITC benefit 

7. you can also tweet on twitter to the GST council. If you are lucky, they may take cognizance

pay amount under protest as you are entitled to benefit of input tax credit 

2) complain to director General of Anti-Profiteering (DGAP)

3) The DGAP  can  Notice under Rule 129 of the CGST Rules, 2017 to the Respondent asking him to file reply on the allegations levelled against him and also to explain whether he had committed violation of the provisions of Section 171 of the CGST Act, 2017 by not passing on the benefit of ITC to the Applicants by way of commensurate reduction in the price of the flat.

4)builder would be  liable for imposition of penalty under the above Section read with Rule 133 (3) (d) of the CGST Rules, 2017. 

The GST Council, on February 24, 2019, slashed tax rates for under-construction flats to five per cent and affordable homes to one per cent, effective April 1, 2019. Currently, the Goods and Services Tax (GST) is levied at 12 per cent with input tax credit (ITC)on payments made for under-construction property or ready-to-move-in flats, where the completion certificate is not issued at the time of sale. 

GST for the complete amount is applicable though you can ask builder to pass on benifit in remaining amount if he fails you can file complaint against the builder before the national Anti- proofertering authority. 

If you took a loan to buy a residential property which is completely build up, and the payment is directly made by your bank to builder then GST is not applicable.

1. You ask for the details from the input tax credit rceived by him for the said period.

2. If it is found that he has really not got benefit of the Input Tax credit, then pay the whole 12% towards GST.

You should only pay the gst at the effective govt rate now.  No payment on inflated gst

If the builder is not giving you the ITC you may issue a legal notice to him about this and warn him to approach RERA and consumer forum if he is not paying the government benefit of ITC to you while he is charging GST.

You can drag him to consumer forum for unfair trade practice.

Dear Client 

If builder is claiming Input tax credit than you can claim it from builder And if he doesn't give you the benefit then you can complaint against builder in GST tribunal.

But builder is not receiving Input tax credit then he cannot pass it to you.

So you have to pay 12% GST to builder. To claim the benefit. 

1. As per the information mentioned in the present query, makes it clear that builder is demanding an arbitrary amount which he is not suppose to.
2. And how is it possible that there will be no GST input tax credit.
3. You should resist to him demands and pay in accordance with the actual percent.