Trying to fight it won't help. They will most likely be able to prove that their calculations are correct, even if it doesn't make any sense. There is a simple solution to this: NEVER EVER hold through expiration Friday where you have no control over settlement value. It's that simple. No need to complicate things. Read more explanation how this works and what are the risks here - http://bit.ly/1cSbAkX
monthly(regular) SPX options expire this week and CBOE, according to their website, is closed for Good Fridayâ Friday, April 18 So, what day will SPX options settle on? Thursday at the close?