Transitional Credit on non - moving inputs

XYZ reversed the CENVAT credit during Excise regime on slow / non – moving inputs for which provision was made in the books of  accounts to write off the same. During GST regime, again re – credit of the same was taken under the transitional credit provisions since there is no such requirement under the GST provisions. Show Cause Notice issued for such wrong availment of transitional credit. Any case law or circular or clarification to defend the case?