This is unfortunate because the mileage is too less for gear box failure. Hopefully, the dealership is cooperating with you and replacing this and the engine in warranty? Also, you shall have to update new engine number on the registration card/book.
This thread is too old and for the early model Sportage, most of which are now running on Toyota engines. So please post in the below mentioned thread for current model Sportage discussion:
https://www.pakwheels.com/forums/t/kia-sportage-dedicated-discussion-owner-fan-club-thread/1119279