Delaying the sale of our house, no accountability on 10 year account

Our home loan which was originally with ABSA was taken over by Nedbank in 2007. Now that we are selling this house, we have been informed that we need documents from ABSA in order for the sale to proceed. It's been over a month that we are waiting on ABSA to find the required documents on their side while they insist that we sign a document taking responsibility for any outstanding funds! How on earth can we be expected to foot a bill that Nedbank took over from ABSA 10 years ago and that ABSA clearly has no records for. Our sale is being affected as it's going on since October 2017. No response and no accountability at all from ABSA. Do not do anything with this bank if you would like efficiency.