Summon under Section 70

Section 70 of CGST/SGST Act gives powers to a duly authorized CGST/SGST officer to call upon a person by issuing a summon to present himself before the officer issuing the summon to either give evidence or produce a document or any other thing in any inquiry which an officer is making.

Both parties to the transaction should be present there.
Documents should be produced as per required by GST authority

The summon says the Supplier is non existent and we need to pay the ITC amount with interest. However we have made the proper payment to the Supplier. What Remedy is available to us in this case. if we pay the ITC amount with interest, being small and legal cost more , are there any other penalty which will be levied?

If possible made an appeal to first appellete authority by showing all the documents with proofs that all payments has been made. But I should suggest that you should pay the ITC with interest