Hi
Is airflow correct?
Is Egr working correctly?
Do you have boost leak?- intercooler under nsf headlight prone for leaks
Is the correct grade of oil been used?
Is the oil at the correct level- repeated non successful regen raises the oil level very quickly on these
Has the oil been saturated with soot due to failure to regen??
Are temp sensor reading correctly??
Has the oil counter definitely reset.?
Has dpf in past been changed for a cheap and cheerful?
Is egr pipe blocked??
ETC

Not the best system to deal with faults can be masked- somethings blocking Dpf, you just need to work out what, after this I would do oil and filter and reset everything

MARK