Sorry to say it but there's the problem - you bought it!
Kittens can be dewormed from 6 weeks old and the vets should still be open tomorrow. If the kitten is refusing to eat anything then it will probably need to be kept at the vets for fluids as it might have health issues. A healthy kitten that is old enough to be sold should be eating solid food ok. Try mixing the kitten wet food with lots of water and syringing a little bit into it's mouth.
Sorry to say it but there's the problem - you bought it!
Kittens can be dewormed from 6 weeks old and the vets should still be open tomorrow. If the kitten is refusing to eat anything then it will probably need to be kept at the vets for fluids as it might have health issues. A healthy kitten that is old enough to be sold should be eating solid food ok. Try mixing the kitten wet food with lots of water and syringing a little bit into it's mouth.