If you feel that the dealership is not taking any of your concerns seriously, then ask to speak with the owner of the dealership that is servicing your Niro. It might take a few tries and a bit of time on your part, but once they are involved you'd find that everyone else inside the dealership will suddenly change the tone and start taking your concerns seriously. If that doesn't work then I'd write two letters (CC:ing each other so they know). One to the owner of the dealership, and the other to the Regional Manager for KIA in your area. If you want it to be taken really seriously, then send the one to the RM as registered mail, so you have a signature for the receipt. Have a log of every complaint that you have, whom to talked to and what they said, did or to your opinion didn't do. Dealerships are pretty regulated by KIA and they don't want bad customer experiences.
Your oil should not be getting any gasoline inside. if the levels are going up then there is a definite leak somewhere and this will have an adverse effect on the lubrication level in the oil. it will lead to the engine needing to be replaced.
2018 Niro EX - Ocean Blue
GTA - Canada.