Product: Debt collection

When we moved out of our apartment at XXXX XXXX in XXXX XXXX, VA. I had went to the front desk to be sure that we would n't owe anything for the carpet in our apartment. We have a dog and cat. I paid a non refundable $ XXXX/month pet fee to cover any pet damages that may occur during our stay. We lived in that apartment almost 4 years. During which time that apartment got flooded from other apartments above and on the side at least 3 or 4 times. 
All the flooding had been reported to the front desk right away. In all the cases they sent in someone to suck out the water from the carpets. Despite the fact that they " took care '' of the standing water in our apartment. I still had mold growing in my closets and on my personal belongings. 
The vast majority of my belongings had white mold growing on them when we moved out. The apartment always smelt musk, I constantly had XXXX, both my husband and I had XXXX that would not subside. I had informed the front desk of the mold issue when I found black mold growing in the closets. They came and sprayed a terrible smelling chemical in the apartment. I asked if we needed to leave and air out the apartment, I was told it was not harmful to animals or humans. The smell made us all very ill for the next couple of days. XXXX. I aired out the apartment as much as possible during the day, but it was still lingering for several days after they treated the black mold. 
The women who lived in the apartment above me, said she had the same issues with mold growth in her apartment. 
My dog had a handful of accidents on the floor, I always cleaned it up and shampooed the carpet immediately. 
So when I asked the front desk when we moved if we would be charged for the replacement of the carpet ... because I knew it would have to be replaced. I was told ; " No, we replace all the carpets in every apartment that have pets to be on the safe side. Any damages caused by your pets would be covered under your non refundable pet fee anyway. And you submitted a non refundable deposit when you moved in. So you wo n't owe anything. '' Several weeks after we moved, I got a bill for $ XXXX dollars. It claimed that my dog so severely ruined the carpet and the cement that both the carpet and cement had to be replaced. This seemed a bit extreme, considering that that apartment had been flooded by water, ( water marks and damage could be seen along the trim ) and the flooding from the other apartment occasions. Obvious damage that is documented to leave the carpet unsavable. And if by some chance my dog really had damaged the floors that bad ( very unlikely ) ... the $ XXXX/month in addition to my rent payment, that I had paid in non refundable pet fees for the past 3-4 years would have been more then enough to cover the cost of damages. So I refused to pay a bill, that I - 1. clearly did n't owe and 2. that I had paid enough in pet fess to have covered multiple times over. 
I attempted multiple times to call the front desk to resolve the issue. They refused to return my voicemails and refused to answer the phone during business hours when I would call. It was clear to me that the company was just trying to get more money out of me, by threatening to send the bill to collection.