Oh, if we're talking about general oathbreaking (as opposed to breaking an oath to uphold the laws) then general criminal procedures outlined below apply. Only the penalties and amends are VERY high because of the severity of a broken oath

If it is clear that they have broken oath OR laws and are just stubbornly refusing to accept it (i.e. saying "I didn't do it" even when it is clear they have) then they face exile - usually voluntarily. Fae look at oathbreakers the same way we look at paedophiles and will drive them out or shun them.

In addition, many oaths are magically enforced which can add its own nasty penalty