Sir,
According to Section 7 (1) & (2) of IGST Act, 2017-
(1) Subject to the provisions of section 10, supply of goods, where the location of the supplier and the place of supply are in––
(a) two different States;
(b) two different Union territories; or
(c) a State and a Union territory,
shall be treated as a supply of goods in the course of inter-State trade or commerce.
(2) Supply of goods imported into the territory of India, till they cross the customs frontiers of India, shall be treated to be a supply of goods in the course of inter-State trade or commerce.
According to Section 8 (1) of IGST Act, 2017 subject to the provisions of section 10, supply of goods where the location of the supplier and the place of supply of goods are in the same State or same Union territory shall be treated as intra-State supply:
Therefore if both supplier and recipient are located in the same state/union territory then such supply will be treated as intra-state supply. Hence the contention of the service providers whose services are availed and charges are paid in Tamil Nadu will be treated as intra-state supply and CGST and SGST are to be paid separately.