Ok when I tried canceling this morning on my PC, the cancel button was grayed out.  I tried canceling via the Samsung Shop app and it worked - sort of.  here's what happened in my case:
On the app, it offered me the 10% discount (up to $100) to be applied to my payment method upon shipping if I elected to keep my order and I would receive an email confirming the discount.  Below it said I would receive $85 off if I elected to keep my order, otherwise press cancel.  When I accepted by pressing keep order, I got a brief pop-up window that read "discount mismatch" that quickly disappeared.  I did not receive a confirmation email.
I logged on to the orders page on my PC and selected help via chat.  After almost 2 hours of chatting with a rep and then a supervisor (both with Middle-Eastern looking names) they told me I would receive a 10% discount coupon upon shipping that was good for my next order.  After going in circles a few times, I demanded next tier customer service to file a complaint and after more waiting, they confirmed the discount would be applied to my order as a refund upon shipping, apologies for the misunderstanding, etc.  They also confirmed that shipments are scheduled to be fulfilled the week of 9/2.  (I don't know if this is only for T-Mobile variants or across the board).
I don't even know if it was worth all the hassle, but as I'm typing this, I received my confirmation email for 10% discount for not canceling my order.