Since this prof was accusing you of plagiarism I think you could have appealed this and taken the case to your department’s head of the dean, why didn’t you do that?

I have a feeling that if you articulated your case well enough the prof would have eventually dropped the issue.

I have to say, this seems like it’s mostly on you not defending yourself. Sure the professor was wrong and being an ignorant ass but you shouldn’t have rolled over like that.