Sounds like you have a verbal contract. You will probably have a difficult time in proving such. You also sound like you may have other issues regarding the habitability of the apartment. Please contact your local state bar office and see if they can refer you to an attorney who will help you on a pro bono basis.
If you have a written settlement agreement with the landlord, you should make sure you keep a copy and send a copy of the settlement agreement to whoever is calling you. If the settlement agreement was put on the record in the court, you should contact the court about how to get a copy of it. If the settlement agreement was orally entered on the record in court, then it is binding and enforceable. It might also be entered in the Court's records as a minute order, so you should check on that.
If a collection agency is calling you, you should ask them in writing to "validate" the debt, which requires them to get information from the landlord.
Finally, below are links for assistance with:
Landlord Tenant Issues