2018 A3 TFSI Hatch rear washer not working, have replavef jet module but still not functional. Very small amount of water comes from washer unit with jet module removed but not enough to even resch rear screen. Any suggestions for a fix ??

Welcome Gary, and thanks for joining. 
If you aren’t getting a good supply to the jet, have you checked the reservoir outlet for partial blockage? Washer reservoirs are very prone to generating undesirable ‘goo’ which restricts the flow by partially blocking the feed. Also possibility of a partial fracture in the tube due to flexing where the boot opens and closes -? 
Kind regards,

Gareth. 
 

In addition to Gareth's suggestion of a broken pipe, check the rear wiper motor for leaks. The water runs through the motor and has been known to leak past defective seals.