After sending a complaint about how horrible the website was functioning the past few days, I got a response email saying that they apoligized and would send me the coupon anyways (even though I could never get through).
But they also said this:
“Be sure to visit drpepper.com often, beginning January 1 we’ll be giving away coupons for a free Diet Dr Pepper! Sincerely, Consumer Relations”
So if the site is terrible then too… use the contact us section to complete the form for comments and mention to them you couldn’t get through. I know they also put up a toll-free phone number but that was busy all day for me too because of the high demand.
Maybe this time it’ll work!