Hi, and welcome.
The 'unserviceable' mesh screen is located at the bottom of the pick-up tube,
under the fuel sender. It is most likely the cause of your issues due to what you've done already.
It can be punctured by using an old long screwdriver, (or something similar,)
bent to 90 degrees an inch from the blade end. Here, a borescope camera would be useful so that
you can see, initially, what you're aiming for.
Once you position the tool, use a hammer to drive sideways through the mesh, at as many locations
as you can.
Borescope again to check your work.
Once you're satisfied you've got a few holes, close up the fuel sender.
It's now essential to fit an additional filter between the tank and the pump, to protect the pump
from future debris.
Hope this helps,
Nigel
