Here are a couple of the articles just to doublecheck what you are doing:
https://www.backyardchickens.com/a/raising-your-baby-chicks
https://www.backyardchickens.com/a/...ks-the-first-60-days-of-raising-baby-chickens
I would contact the hatchery again. Sometimes there can be bad batches of chicks, and sometimes they are not shipped safely. So much can happen to them. Even the ones from feed stores can suffer the same shipping stresses. Brooder temperatures can fluctuate all of the time inside your house or in the coop. Temperatures may cause them to huddle together under a lamp for warmth or try to get as far away from the heat if they are too warm. I spend a lot of time watching them the first 2 weeks. So sorry for your loss.
https://www.backyardchickens.com/a/raising-your-baby-chicks
https://www.backyardchickens.com/a/...ks-the-first-60-days-of-raising-baby-chickens
I would contact the hatchery again. Sometimes there can be bad batches of chicks, and sometimes they are not shipped safely. So much can happen to them. Even the ones from feed stores can suffer the same shipping stresses. Brooder temperatures can fluctuate all of the time inside your house or in the coop. Temperatures may cause them to huddle together under a lamp for warmth or try to get as far away from the heat if they are too warm. I spend a lot of time watching them the first 2 weeks. So sorry for your loss.