Need Zendesk advice for "Failed to authorize payment"

I am trying to port-in a line from T-mobile to get the free LG Spree.

I have repeatedly received the "failed to authorize payment" message. I've tried 3 different browsers and 4 different credit cards. I've tried playing with the billing address to no avail.

Contacted zendesk and the rep was not very helpful. He advised to do it in store, but the stores here are authorized retailers, and they want to charge an extra $25, plus they don't want to honor the free LG spree promo. So it will be an extra $100+ to do it in-store.

Is there any way to reach a zendesk rep that can push the order through?

Thanks guys.