I am not sure if this would work, but if you have a Vet school in your area they may have a free or discounted clinic. There is a member on YT that is in Vet school, maybe she would know.
I know when humans have n/v and diarrhea their electrolytes go out of wack and that can cause seizures. Are you giving anything to replace the electrolytes?? One site recommended pedialyte mixed with chicken broth to make it taste better and I saw another product called rebound.
I would visit the rescue if possible since you can't get them on phone.
Good luck with the vet visit. Maybe you can take a long nap while you pup is there. Keep us posted on your baby's progess. Hope all this ends for you soon!
ps if you have more than one dog, i would separate them until Kobi is better!