As per article 20(2) of our Constitution, no one can be punished twice for the same offence. How this is relevant in terms of GST law?

Offences for the purpose of this article mean criminal offences. Proceedings in GST laws are in the nature of administrative enquiries. These are different from the proceedings in a criminal court where the enquiry is on the basis of evidence tendered on oath. Since tax penalties and prosecution are not considered to be criminal offences, one can be prosecuted under both GST laws and SEZ laws for same offence (say for clearance of goods).