Can I get a refund for a dog I purchased from a private breeder

I purchased a dog that ended up being hypoglycemic. I was not made aware that the dog was hypoglycemic at time of purchase and after 2 visits to the vet the dog died within a week. I brought it to the sellers attention and was promised first pick of the next litter and replacement of the dog. Now the seller is saying he will SELL me another dog for half the sale price and that I can not have a refund even though I have text proof of promise of first pick of the litter and witness to the conversation we had when we sat down with the seller.