Apparently, there is no delete account option at all. Seems a bit strange for a company that is supposed to be "disrupting" fashion.
Looks like people have been upset about this for several years now too and nothing is being done about it.
https://www.facebook.com/stitchfix/posts/how-do-you-actually-cancel-the-account-i-never-want-to-receive-a-fix-ever-what-d/1104202652998691/