harassment or threats? (Illinois)

State of Illinois: A customer has complained to my boss that I harassed her and her family and she felt threatened while I was working. They owe me money and when I saw her I asked if she was going to pay and she didn't respond so I said "See you in court, have a nice day." She says she feels threatened by this although I've already sent three demand letters and let it be known I was going to file small claims months ago. My boss thinks she doesn't have a valid complaint, but 2 weeks later they submit a letter to my work stating that I harassed her and her family. Is what I said a threat or harassment? I certainly wasn't talking to her kid. I do intend to sue her. They (her and her husband) want something in writing put in my work file about their complaint. What is the definition of threat or harassment? If they keep complaining do I have any recourse? I'm feeling kind of harassed myself, and they also said they would embarrass me in court to dissuade me from filing.

Saying your going to court is not harassment.

...but quit talking and file in small claims...