DSLAM ports cannot be changed willy nilly. If a port change is required it has to be authorised and the change done centrally as well as at the cab , otherwise the port wont work. They original port will be marked as faulty for investigation. Eventually the ports will run out and the faulty ports checked and repaired.
The engineers have explained that and one even asked if he could move my connection to the other cabinet, which is getting 110Mbps feed, but this was refused.
From what I have been told by some of the engineers, no matter what port they have used since my first port change, the speed they are measuring at the ports in the cabinet is only around 48 - 49Mbps even before it goes any distance down the line.
The fact that they are only getting 48 - 49Mbps at the DSLAM port highlights that the DSLAM is the source of the fault as the speed at the port should be close to the maximum speed. I can only go by what I am told.