2nd mortgage charge off

I have a question: I had a 2nd mortgage with Chase Bank, had made arragements to catch my 2nd mortgage up with them by making double payments for 6 months and after giving them money up front, I had made all the payments but had filed bankruptcy in the midst of it. After the bankruptcy was over, Chase refused to reaffirm with us and called me to offer a settlement and I told them that I needed to speak to my husband about it and would get back to them in a couple of days. Before I could get back with them, they sold the mortgage to another company and placed my status with them as a charge off. After making several payments to our new mortgage company, Chase called us back and told us to cease making payments with the new company and start making making payments to them, We, in turn, contacted our new mortgage company to inquire what was going on, they faxed us a copy of the paperwork showing that they owned the mortgage and to ignore Chase. After a few weeks, the new company was able to prove to Chase that they owned the mortgage and Chase stopped harassing us for payment. My question is this, if Chase sold our mortgage to the new mortgage company how can they list it as a charge off? 2nd question: how do we know for sure what they sold the mortgage for since they have it listed as a charge off?