Refund /set of cvd and sad paid towards excess import under advance authoristion after gst

We have paid Rs.150000/- on 20.7.2018 towards Customs duty payment for excess import made in the Advance Authorisation in the year 2015-16.The Customs duty structure is Basic Customs duty 10%+CVD 16%+Edu.Cess2%+Second.Edu cess 1%+ Special Additional Duty (SAD) 4%.When Ecxise was active we could have claimed CENVAT againt CVD and SAD but,now in GST how we can claim to get refund or Setoff CVD and SAD paid??? .