In most states, and under most leases, hindering a landlord from renting a property through informing prospective tenants of problems you've experienced is illegal, and can result in you being forced to pay damages to the landlord for making such claims if they are unable to re-let the property. I recommend against taking such actions.
You do seem to have an argument that the property is uninhabitable. Unfortunately, you can only use this argument to break a lease early. If you don't currently have a lease, you effectively have no rights to be there, as a tenant or otherwise.
Despite your issues, you have chosen to keep living on the premises, and you are legally required to pay rent while doing so, meanwhile the landlord may evict you at any time. Your rights as tenants have ended. Proceed as if you have none. If you've overpaid your rent, you're entitled to its prompt return once you leave.
You've said you can't afford to move. It actually sounds like you can't afford not to move. If you're evicted, you will no longer have any control over the timing of your vacancy. I would recommend telling the landlord that you are looking for another place to live, and will vacate soon. This will probably stall any forthcoming eviction action on the part of the landlord.
Essentially, be adults and be honest with each other about your intent, and firm in your expectations and demands (like the excess rent you've paid and want to use). Usually some sort of deal can be reached that's better for both sides than having to go to court to work it out. Some people (your landlord, for example) may need to be reminded of this before they are willing to reach such an agreement.