Re-opening your case is going to cost you at least $150 filing fee and could be more depending on what happens. The court may not even agree to re-open if they agree with the case law that says all pre-petition debt in a no-asset ch 7, whether listed or not, is considered discharged.
I'd try sending them letters first telling them you filed BK, list case number, filing and discharge dates, and that attempting to collect on a discharged debt is illegal. I'd try that tactic first, if they still harrass you, try to re-open your case to add them.