That is odd for an extract kit, and like @jake said, that is poor attenuation for any yeast really. I've had stuck ferments in the past and tried a number of things.
I've tried pitching more yeast, unfortunately I read after the fact that unless you pitch a yeast starter at full krausen it is unlikely to help. It didn't help at all with mine. I have also tried adding yeast nutrient but that didn't help either.
Depending on your temp you could warm it a little to see if that gets things going again.
You could wait a week to see if your numbers improve at all before starting to mess with it.
If you're concerned about this happening again I would ask them to sub out the yeast in the kit for US 05. It is a neutral strain, but it always attenuates well.
If you get desperate, eventually, you could always transfer to a glass carboy and pitch some brett. It would take time but it would eat up those remaining sugars.
Keep us updated on how this goes.