Put it simply someone used your account with a credit card, got RP, probably transfer it to another account and the charge back the money so riot suspended/ban your account to get their money back.
that someone could or could not be you, I really don't care but that is the gist of it.
If it wasn't you and you prove it wasn't you then you will get your account back after a few mails back and forth. If it was you then just pay the money and you shoudl be fine. Anyway for $10 is usually better to just pay the money that go though the legal loops to get your account back without paying, from my point of view the time spent to prove it wasn't will be worth more than $10 but is just my opinion...
Regardless, if you pay don't follow up any link from the email and instead do it through the official website just to avoid running into well made scams. After you get your account back remember to change your password and probably do the same with your email password and probably check your PC for spyware just to be on the safe side.