Okay, so I know it's wayyyy too late to talk about Destiny 1, especially when Destiny 2 has just released, but how long has it taken anyone to get the Age of Triumph Shirts, from reaching Rank 7?
I know it's supposed to be 3-4 weeks, but I've waited about 5 weeks on my order, and I'm pretty sure my shirt was supposed to come 2 weeks ago; I ordered July 30, of 2017. At the time, the code T17-NXJ-3C9-4C7-NF9-YMK was the code I entered into the system, and I managed to get a Medium-Sized shirt, although without any username imprint.
I think it's pretty bad that it's taking this long, but I think it'll be worse if Bungie misplaced my order, because then that meant I just wasted 30 dollars on a T-Shirt I never got.
Email the Bungie store. The forums are for the game itself, not merchandise so you're not going to find any help here about your shirt.
It took 3-4 weeks for mine to come in. Your's might take longer since you ordered near the deadline.