Trade in problems lead to a downpayment

ATT is asking me to pay a down payment upfront on a new phone I am receiving a full credit for with an eligible trade in. Additionally, I was already able to order the form and pay the tax, but a phone number port transfer problem held up the shipment and ultimately cancelled the first order. I have since cleared the port transfer problem but now when I re-order they are asking for a 328 dollar down payment. (Can anyone make since of this?)