Product: Debt collection

The leasing company XXXX XXXX has put a collection amount of {$1100.00} on me and co-signer ( my son ) without any notice. They are supposedly charging us a fees that we were never told about. 
We left the apartment in the condition we received it ( un cleaned ) we requested cleaning by emails but never happened, and when we turned over the keys to the office at the end of the lease, we made sure there was nothing owed and they had us sign communication form has all our information ( address, phone, email ) incase they had to contact us in the future for any missing or a problem.

And then My co-signer found the collection on his credit report towards the end of XXXX, Keep in mind at this point there has been no notice or any form of communication from the leasing company or the collection agency informed we have an amount we have to pay, When we contacted the XXXX XXXX on XX/XX/XXXX to figure out what the issue was, they told us they had supposedly sent us an email of the closing statement but they never did and a physical mail copy in XXXX as a notice. We never received a copy or an email relating to this matter prior to us contacting them. We talked to the assistant property manager and not only was he very unprofessional, he kept trying to end the call without resolving the issue, we asked him to resend the email about the closing statement and he never did. 
We then asked why they waited until XXXX to send us a physical mail considering we moved out XX/XX/XXXX ( at the same time we checked the collection details was posted in our account on XXXX ) they posted our collection a month before the assumed contacted us, and the manager said that there was a delay in the office. We proceeded to tell them that it was their mistake not ours and that we should not be charged those ridiculous fees including a cleaning fee, and a wall painting fee and other fees according to what they assumed without any approve invoice. Those actions were voluntary and not because of any sort of damage found on the property. When we first moved in, the apartment was very dirty so we had asked if they could send a cleaner and they never did. We asked 3 times by email and even the main property manager even acknowledged that they never sent one and apologized for not cleaning the apartment, so we had to clean it ourselves. There was damage on the property before we moved in that was all documented on a sheet they had given us. There were scratches on the wall, on the floor, in the bathroom, bedrooms and we reported it. There were many spots where the floorboards made creaking noises in the living room, bedrooms, and the kitchen. We had made maintenance requests about the front door because it would lock us in sometimes and no one would be able to get in or out. We had to call management multiple times just for them to fix this issue. There is a foundation problem and its has a big walls and ground crack in this property, very dangerous and not safe for human being to live in, we are wondering how the city of XXXX approved the building all sorts prior to us moving in that was documented and we should not be charged because of that. They dont want to cooperate with us or show us any evidence or proof of what theyre saying, an addition to all above the collection sent to ( Rent Solution Recovery ) we contacted them many times never comeback to us and they were a scam there is over XXXX review they talk about the same issue.