I made the mistake of cheating on my girlfriend a year ago and now the girl I cheated with is taunting and harassing me?

I got involved with someone a year ago behind my girlfriend’s back (yes, I know it was wrong). I made the mistake of not telling the person I got involved with about the fact that I had a girlfriend. She somehow found out and ghosted me, now my girlfriend and I are being harassed.

She (anonymously) posted about me to a FaceBook group called “Are We Dating the Same Guy?” and friends and family members are questioning me about if I’m seeing someone else (although I’m no longer seeing her or anyone else). She requested my girlfriend as a friend on IG and FB and my girlfriend keeping getting phone calls from her. My girlfriend keeps asking me who she is and I don’t know what to tell her.

Should I file a police report?
I made the mistake of cheating on my girlfriend a year ago and now the girl I cheated with is taunting and harassing me?
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