On what grounds did you replace the DPF?

I have had this issue, and it is not actually that hard to put right, but there is no way I would have replaced the dpf before at least trying a forced regeneration.

In my experience the differential pressure sensor is at fault, and a forced regen is required to complete the job.
Obviously your car should be assessed on its own merits, but one has to feel for the unwitting customer on jobs like this, can you be sure it required a new filter?!
If you are sseing VAG regularly VCDS is essential also.

HTH, let us know your diagnosis procedure.

Liam.