Oh, gosh. Please try to forgive yourself. You are a very careful shopper and these things happen.
I'm glad you are going to try customer service for both. Let us know how the companies respond -- useful info for us all! I do think if an item fails after you wash it according to instructions, that is a quality control issue and not your fault. And footwear is just so hard to predict!
My biggest fail this year was footwear. My fab (haha) white sneakers that turned out to give me awful blisters no matter what I did -- socks, bandages, different insoles, heel guards -- the works, but nothing, nothing worked. There is nothing for it but donation.
Another fail: an Aritzia shell top, thrifted -- not worn. Not expensive, true, and theoretically a useful item for me, but I don't know...every time I put it on, I ripped it off. I have an identical top in off-white and wear it a lot. Why. not this one? Something about the fit is slightly different. So it is a similar situation to your boots. I thought I had a slam-dunk, and instead I have a big miss.
Oh, and I bought the Cole Haan loafers on sale as inside shoes (slippers with better support) because I loved the oxfords so much. But guess what? I am not wearing them at all. I just don't enjoy them. They fill the easy/on/easy/off box but they feel frumpy on my foot and they slip off quite easily. And look cheap. Whereas the oxfords don't (to my eye). Anyway -- there it is. My confessions.