Brand-New Munchkin 12+ Month Sippy Cup Leaks Every Time and Soaks Couch

I purchased a 12+ month sippy cup directly from Munchkin’s website. I previously used their 6+ month cup and was very satisfied with it—especially because it was completely leak-proof—which is why I chose the brand again. However, the new product that arrived today has leaked every single time since I started using it.
Even though I close the cup normally, water constantly leaks out and left my couch completely soaked. I thought I might have secured the lid wrong, but after carefully trying multiple times, the result was the same. Because of this, I believe the item is defective or has a manufacturing flaw.
Since this product has caused problems from the moment it was delivered today, I am requesting an urgent replacement or a full refund from Munchkin. Additionally, I cannot even access the return/exchange section on their website, which makes this experience even more frustrating. I ask for a quick resolution to this issue and a clear response.