Yes, you can refund data packages. To refund a data package open Nommi app > Profile page > My packages > Select a data package > Refund.

Terms of a Refund:
Data packages are eligible for a refund within two months after the purchase. Refund commission is 5% of the total cost of the package. Nommi automatically refunds all the packages that have not been used within 2 months since the purchase.