Im sorry to heard that.. You can try STP Tuff Stuff. It's a multi-purpose foam cleaner. It will be much easier if you can take out your seat, use the STP cleaner and wait until it dry.. Direct sunlight will be better.. my 0.2P
just remove the seat from your car and just wash/spray the whole seat with warm water and a small amount of dish washing liquid until the stain dissolved.
then place the whole seat under the sun to dry, turning every few hours to throughly dry the seat. use a fan at night to blow at it. be patience as it may take a days to dry.