When I got perma banned on my first account I contacted support and they refunded all of the RP I hadn't spent yet. If you still have RP on your account contact riot support and ask if they can refund it.
You won't get your money back, but check if it a permanent ban or temporary, you should also check your mail why you got the ban maybe you can ask to cancel it if it given to you by a mistake. contact the support. https://support-leagueoflegends.riotgames.com/hc/en-us
https://support-leagueoflegends.riotgames.com/hc/en-us