Trade-In Device

On April 30th, I ordered a new device for a line on my account and subsequently entered the information to trade in the old device. I received the email with 2 attachments needed to ship the device back. I opened the first attachment, which contains the information for the trade-in. The second attachment, which I believe to be the shipping label, does not open. I receive a message that says "something went wrong, try again later." I have contacted XFinity mobile 3 times now and each time been given different information. Twice I have been told there is no record of a trade in on my account, despite the fact I have an email with a document that says otherwise. What do I need to do to get this shipping label to mail back the old device? It needs to be mailed back by 5/21.