@Ladan Ballai This is all very clear to me. I think the only path you have is what others have already outlined, small claims court, if it comes to that. Likely, this entire even will have some level of monetary cost to you.
I own many many rental properties and ever single property i have ever purchased was already rented. Obviously, i have always reviewed all tenant agreements prior to making an offer. I have also on every purchase met all of my soon to be tenants, prior to closing, to go over their tenant agreement, among other things.
I would never take the words or signed documents of current owners and tenants as be all end all! I want to look all parties in the eyes and see that we all have the same understandings of all the contracts. Ive' even gone as far n some cases as having a notary come in and we all sign together and update the contract with new signatures.
This is just food for though should you ever purchase more rental properties.