Disallow u/s 40(a)(ia) on account of non-compliance with the provisions of Chapter XVII-B

The assesse is a partnership firm engaged in the business of Construction work. For A.Y.19-20 they received demand for disallow u/s 40(a)(ia) on account of non-compliance with the provisions of Chapter XVII-B. They incurred labour cost worth Rs.51,00,000/- debited to profit and loss account on which TDS of Rs.51,000/- deducted on 31/03/2019 and paid in the month of October 2019 and filed form 26Q on 25/10/2019. The department has nade addition of Rs.15,30,000/- and raised demand for the same. The ITR5 was filed after payment 28/10/2019 and extended due date was 31/10/2019. Please advise.