Nighthawk M1 Firmware problem after update with Dashboard

Hi, My Nighthawk was a wonderful thing until it did a firmware update, since then it has been basically unuseable. If more than one device is connected it slows to a crawl & will not open pages most of the time. Telstra have been no help as the "cannot" rollback the firmware & have sent the unit away for testing and been retuned "no fault found".

How do i proceed from here, i have spent hours on the phone to both Telstra & Netgear support with no joy.

Have tried all the standard phone operator suggested fixes, No change.

this unit is now unfit for purpose & is costing me money.