If you go into a movie theater and buy a ticket to see Finding Dory but halfway through the film decide that you don't like it and proceed to proclaim your dissatisfaction at the top of your lungs, you will be kicked out of the theater. You will not be refunded, you will not be treated kindly at all, in fact.
Why do people expect refunds when they're banned from league? It's the same principle. You're paying for an entertainment service. You are not buying a good for you to own. If you break riot's rules you get kicked out and cut off. You gave them your money and now it's their money and still their service.
TLDR; RIOT WILL NOT AND SHOULD NOT REFUND ANYTHING IF YOU ARE BANNED FOR BREAKING TERMS OF SERVICE