Can't upgrade at all through any third party retailer

After a weird order that fell through with Samsung, retailers can no longer upgrade phones on my account. Even when paying in full, I get the following responses trying to buy a phone through online retailers:

- Apple: "You're not currently eligible" - Best Buy: Orders just dont appear in the cart and customer service can't add either - Samsung: "We ran into an error, try again later"

Does anyone have any idea what this could be? T-Mobile customer support just says that since they could place an order, everything is fine.