The revenue department has unearthed as many as 931 fraudulent GST refund cases through data-analytics, which has forced it to scrutinise all the past refund claims for inverted duty structure that are already settled, along with the pending ones. In the current year itself, refunds of over Rs.28,000-crore have been filed by over 27,000-taxpayers on account of an inverted duty structure, said the source.