Hello.
I will try to help you with this but I need more information first.
What state are you in? When did you move out, and when did the lease expire? What did the attorney say about terminating the lease, and what sort of notice did you give the landlord?
Do you have the results from the petri dishes, and if so, what do they indicate? (E.g. elevated mold? what types of mold?)
Do you still have effects of asthma or migraines that are due to the mold exposure? And do you think your doctor would be willing to testify for you in court on this issue, if necessary?
Do you have an attorney representing you now on either (a) the debt to the landlord or (b) your mold exposure?
What has the landlord done to come after you for the rent? E.g. have they sent you a demand letter, or have they sued you?