Landlord/Tenant Dispute. Need help!

Hey LegalAdvice, tenant here.

About a year ago, my fiancee​ (now wife) moved out of a small townhouse in Missouri. A couple of issues happened. The first issue, was that the Landlord refused to do a walk-through after 5PM or on weekends. My wife and I both worked day jobs, and couldn't afford to miss. They wouldn't work with us.

We had known there would be some pet damage. We had a pet that had ruined a considerable amount of carpet. When we moved in, we paid 400 in pet deposits as well as a 400 dollar security deposit.

After the inspection, we got a letter in the mail at our new address. They were trying to charge us 1600 dollars for the damage. We looked at the attached receipts, and 500 dollars was from "Loss of Income." They argued that since the repair took 15 days to complete, they missed out on potential renters for that month. They also charged us a 250 dollar cleaning fee. The actual repairs totaled 740 dollars, which is what we had expected. We spoke briefly to an attorney over the phone, and he recommended we sent a reply via mail that we wouldn't pay "Loss of Income" or the Cleaning Fee (my wife called prior to the move out inspection and the desk lady told her they were charging a standard 250 dollar cleaning fee regardless of the shape of the apartment, which to my knowledge is illegal in the state of Missouri. It also wasnt in our lease.

We sent a letter arguing the sum down to 800 and calling it even, since the repairs only costed 740 dollars. We figured that worst case scenario, they take us to Small Claims.

We received a later back, and they dropped the cleaning fee, ate our 800 dollar deposit, a were demanding 535 dollars for "Loss of Income" still. We refused to pay it, and instead of filing a Small Claims court battle, they reported it directly to the Credit Bureau and ravaged my credit.

If anyone is experienced with Missouri Landlord/Tenant Law, would it be worth it to fight them in Small Claims for them to drop the $535, or even to lawyer up and sue for ruining my credit with no legal backing? According to the attorney we spoke to, "Loss of Income" is virtually unprovable in court.

Edit: I Should also specify that the receipts were dated several days apart. It looked to us that judging by the hours spent on repairing everything (a few hours) that they could have completed the repairs in one day.