Open Source License Compliance — fanfiction and derivative works

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

fanfiction and derivative works. I've been dealing with this for about 12 weeks now and the situation isn't improving.

This involves software/code I developed over the past 6 months. I do have documentation proving my ownership and timeline.

Should I hire a lawyer for this or try to handle it myself?

Attorney here. Here's my take on the legal issues.

There are several legal theories that could apply here. The strongest is probably 17 U.S.C. § 106, which requires showing substantially similar.

Before taking legal action, consider sending a formal demand letter. In many cases, this alone resolves the issue.