Didn't receive the return shipping kit.

I made a trade-in of my iPhone 13 for my new iPhone 16 about two weeks ago, and I received iPhone 16 already. But I still didn't receive the return shipping kit to pack my old device, and I've called the T-Mobile for several times, when will my return shipping kit deliver to me! I only get a week to return it to able to get my bill back for trade-in.