Bests & Worsts Reviews from Amazon

At first I really liked this cup, it kept my water cold and ice stayed intact for at least 8 hours. The lid is a little difficult to remove though. But then, after less than a week I noticed rust in the bottom of the cup. I contacted the seller and was told just to return it to Amazon but I wanted to reach out to Hydro Flask directly because all of their products are supposed to have a warranty. After 3 days I received an email back telling me to scrub it with baking soda paste and if that didn't work I can send in the product for an exchange but I would be responsible for shipping. Since the rust is right on a seam, that would lead me to believe it is a manufacturing defect and I really don't want to have to scrub it with baking soda paste every 5 days. I have had a 22 ounce Hydro Flask for 3 years and have never had any issues with it whatsoever. I am extremely disappointed in this company (Hydro Flask, not the seller here on Amazon), if I am going to spend $40 on a drinking cup with a warranty why are they not willing to stand behind it?