I'm sorry you are having to deal with such a difficult & perplexing problem. I don't really have any particularly useful suggestions to offer. But I noticed no one had yet replied to your post. So I thought I would.

I searched PsychCentral's archives for something related to this but could not find anything. I did find one webpage that discussed the problem. Here's a link to that webpage:

When People Say You Always Looks Angry/Upset/Worried/etc | www.succeedsocially.com

Beyond the kinds of things that are suggested on that webpage, I guess what occurs to me is that perhaps one alternative would be to focus on the social anxiety you are experiencing. There may or may not be a lot you can do to change the way people interpret your resting face. But social anxiety is a condition that is treatable. So here are links to 7 articles, from PsychCentral's archives, on social anxiety... the first by DocJohn:

Social Anxiety Overview

Social Anxiety Disorder Symptoms

Social Anxiety Disorder Treatment

6 Ways to Overcome Social Anxiety

https://psychcentral.com/blog/7-ways...dium=popular17

https://psychcentral.com/lib/4-psych...ocial-anxiety/

https://psychcentral.com/lib/book-re...dium=popular17

Best wishes...