Because this is the lowest-hanging fruit imaginable, why not take the 5 minutes to add a robots.txt and then use https://www.bing.com/webmasters/robotstxttester to confirm that Bing can fetch/parse it?
You're certainly getting a lot of free SEO help today. I'm not the one who has problems getting my site indexed, but it seems like they are different things.
# Allowing all web crawlers access to all content
User-agent: *
Disallow:
