Anyone here gone through open source code in commercial product?

I publish illustrative scenarios prepared by my practice. All participants and conversations are fictional. The fictional posts are not posts by real users, accounts of client experiences, or reports of actual results.
Illustrative scenario prepared by my practice.
For informational purposes only. This is not legal advice. Laws vary by jurisdiction. Consult a qualified attorney for advice specific to your situation.
Hypothetical question

Has anyone dealt with something like this? I'm not sure what my options are.

open source code in commercial product. I've been dealing with this for about 5 months now and the situation isn't improving.

This involves software/code I developed over the past 18 months. I do not have documentation proving my ownership and timeline.

Do I have a strong case? What should my next steps be?