Onlykittens.in - Pet shop falsely sold dying kitten with infection

We bought a Maine Coon kitten * months old from Onlykittens.in on *th July ****. The seller assured us that the kitten was completely healthy and we paid INR **,*** and the kitten was delivered to us on **th July ****.
The kitten was weighing *** gm as per their health certificate on *th July and when we got the kitten tested with our vet on **th July during delivery, he was already weighing *** gm which is **gm weight loss in * days. The kitten also had ear mites which the seller had not informed us before. We took the delivery assuming weight loss could be due to travel stress, but within * days the kitty started vomiting continuously and weight dropped to *** gm. On diagnosis we realised that the kitty was infected with Giardia and other deadly bacteria which it had got from other animals at the pet shop. Kitten continued to puke and lose weight excessively and passed away on **th July despite all out efforts on treatment to save the little one.
Clearly the seller had lied to us about the health of the kitten and sold us a dying kitten. Even if they had informed us on day * of purchase, we could have probably saved the kitten.
I want Onlykittens to be held morally responsible for such fraud and not being transparent in the transaction. My family and I have gone through a lot of emotional trauma in the last * days and want Onlykittens to refund us the cost of the kitten plus the medical treatment cost.