Banks error from 11 years ago costs me money

My parents are in the process of selling their house to me. In 1998 they signed a surety bond for me over another property. This property was sold 11 years ago but Nedbank did not cancel the surety bond. We have been trying since March to get this cancelled with no luck. We this week received a notification from Nedbanks attorneys that nedbank had advised them to stop the cancellation of the bond. There is no money outstanding and other property was sold! No-one seems to respond and this is holding up the entire transfer resulting in 3 different groups of people having to pay occupational rent. The service is shocking for a mistake that was clearly made by the bank 11 years ago! We even have letters from the bank stating they have cancelled the bond then they instruct the attorneys not to cancel it!