They have anti-cheat's implemented in game level and server level. They do not need to see the screenshot for proof, as everything in the game is logged. If they say this it is "legit", I would let it go and just move on.
Send a ticket to the Customer Service. I feel this post will help you: http://forums.racingrivals.com/rivals/discussion/206503/looking-for-assistance-account-issues#latest
It is just a business thing. You purchased them at that time weather or not they were glitch at that moment. Legally everything in Racing Rivals is the property of Carbonated. So I doubt you will see a refund and would probably be better off just eating the mistake. I understand and it sucks that it happened to you, but…