Phone upgrade discount

[Wakeley Bridge]

I've had several talks with Straight Talk in regard to receiving a discount when purchasing a Samsung S5. I'm a very long term customer and was told that an upgrade to this phone at the current price listed $529 would get me a $50 discount on the purchase. I asked for a promo code to use when placing my order and was told that it would automatically appear at the checkout page when purchasing. So, I tried to place an order for the Samsung S5 on the internet web site and got clear to the final page of the ordering process and no discount ever appeared.

How do I order this phone with the $50 discount that I was assured was due to me?