I’m not sure what else to suggest, other than to reset it again. Do you ever type your last name in all caps, for whatever reason?
I find that autocorrect is quick to learn something, but getting it to forget something without resetting it is almost impossible.
One last thing to check. Go to: Settings > General > Keyboard > Text Replacement. See if you can find your last name in all caps anywhere. If so, delete it by swiping left on it.
If you don’t find this helpful, simply start a new thread; there is much combined knowledge here, and someone may have another idea: https://discussions.apple.com/post/question?communityId=2044020