I think the best ways is to do a partial or a DNA, or say that something with the product is not good, like a broken package (easy fakeable for photos), or say that the product is grumpy and has humidity inside (harder to se).
One time they sent me the order in 2 different boxes. I took advantage and said that I only received some products (what were inside one box), and it worked right away haha (doubled everything on the other box).
Saying that you feel bad after consuming, tried that, they will ask for the reference of the product, and will analyze the whole batch. At least I tried this with other company, and after one month they just said that the batch was good, and they couldn't do anything about it.
It could work for myprotein, just try and let us know how it goes