Starbucks Ice Brown Sugar Drink Made with Regular Milk Instead of Oat Milk

Just tried out the Ice Brown Sugar drink at Starbucks and made sure to ask for it with oat milk, just like the original recipe calls for. Unfortunately, I was billed an additional fee for this replacement and was given a drink made with regular milk instead. I'm confused as to why a coffee that's usually made with oat milk would be prepared with regular milk instead. I hope the necessary individuals take swift action to address this matter and offer a solution. As a devoted patron, I feel that a well-regarded coffee brand such as Starbucks should place a high importance on ensuring customer contentment and refrain from engaging in any activities that could erode trust.