<h1>IndiGo seeks Rs 900 crore refund for Customs duty on aircraft engines re imported after overseas repairs under double levy claim.</h1> Petitioner challenges re levy of Customs duty on goods re imported after overseas repairs as a double levy where basic Customs duty was paid on re import and GST was discharged on the repair service; petitioner seeks refund of over Rs 900 crore paid on more than 4,000 bills, relying on a tribunal ruling that re levy is impermissible and that a later amendment to an exemption notification operates only prospectively.