Smashbox - How to break a customer's trust

Smashbox sent me a promotional offer of 15% off my first order (woohoo), so I placed an order. The discount code wasn't applied, and I immediately queried that with customer service. They replied over a week later, saying that I was sent samples, and as only one offer applies per order, the discount wasn't applied.

I specifically selected the discount offer, by entering in the code, but the sample offer was chosen for me. So why widely advertise a discounted first order if it's not going to happen? And then customer service takes over a week to reply? I find that deliberately misleading and disingenuous.

Plus - other makeup companies routinely send samples with orders above a certain value, and that doesn't negate any discounts or offers, so it's not like it's common practice.