As an investor, the builder's claim to deduct GST from your payment raises concerns. While the builder may have paid GST on construction materials, the GST on the sale of an under-construction property is typically the buyer’s responsibility, not the seller/investor. Additionally, if the builder is deducting GST, he should provide a proper GST invoice and have valid GST registration to substantiate the deduction. Without proper documentation, such as a receipt or GST invoice, the deduction seems questionable and may not be valid. You may challenge this legally or consult a tax expert for further advice and remedies.
Are you considering involving a tax consultant or legal advisor to help you with this situation, or do you plan to resolve it directly with the builder?