Chorusnz: The 300mm depth referred to in other posts is for 20mm PVC duct.
If the ruggedized duct was laid using a slit-trench (alongside the path edge) then it should be 200mm deep, which is acceptable practice. However, as the OP has discovered it requires very special attention when waving a spade or shovel around. If you are considering overlaying the duct route with 20mm green duct, then you can find the lay recommendations online at: https://www.chorus.co.nz/land-development/subdivisions/installig-underground-telecommunications-lead-ins-for-urban-premises the standard depth should be 300mm. Once the new duct is in place you can call 08004network and ask for the lead-in to rerouted via the new buried duct.
whats the recourse given it was not buried that deep and now its damaged. give from their account they were being careful, its just that the ducting was only 80mm deep.