Windex is also an option for removing some kinds of marker stains.
I use a product called SoilLove to remove stains that other commercial products can't touch. It's especially good on organic things like baby food, other less pleasant stains, etc. You can buy it online.
Did you try hydrogen peroxide?
Note: I would NOT layer these attempts on top of each other since one may react with the other.
I would stay away from ShoutOut and Woollite since I think they contain bleach-like products. (I've had things fade or develop holes later on or after repeated use.)
Good Luck!