One thing which often gets overlooked is Soundcloud. If you upload your song to Soundcloud it will get date-stamped and it's as near to proof of copyright as you're going to get.

The next thing is that very few individuals can afford to defend their copyright. If your song is stolen, it will likely be by a corporation and if you instigate a legal action against them and lose, you will be liable for their costs. This can run into six figures and people have lost houses this way.

The best you can hope for is a threat based on your Soundcloud evidence and hope for an out-of-court settlement.

Just saying ...

ROG.