I'm not following the landlord's connection to this matter. But at any rate, if these people will testify to what they were told, you don't have a slander case, you have an unfair debt collection case. Contact a consumer law attorney to explore your rights here. You should be able to find a consumer litigation attorney here on Avvo using the "find a lawyer" tab. If you cannot afford an attorney (but keep in mind that some lawyer will take these kinds of cases on a contingency), then call your local Legal Aid office to see if you qualify for assistance. You may also make a complaint with the Consumer Affairs division of your Attorney General's office. Best practice would be to get some evidence preserved here so it would be essential to get an Affidavit from these witnesses early in the process. They can perhaps call contact people but they cannot call and state that you are going to be jailed. Again, consult with a consumer law attorney ASAP and start taking measures to pay whatever is actually owed as well.
It is impossible to give specific answers to questions without meeting and fully discussing all of the potential issues that may not be addressed by your question. The answer(s) provided should be considered general information and are not legal advice. Viewing this information is not intended to create, and does not constitute, an attorney-client relationship. The answer provided is intended to educate you and point to issues for you to raise in a consultation with a lawyer. You should not take any action that might affect your claim(s) without first seeking the professional opinion of a licensed attorney.
A roundup of the best tips and legal advice.