We have an issue with a dentist who has done works (X-Ray etc.) which hadn't been ordered. This has been part of a process for possible dental brace: The task was to identify options and provide a cost estimation but (confirmed by other experts in the field) the tasks he performed were something which should have been done at a later stage after coast estimation and written order from the patient.

Now we got a reminder for the unjustified invoice (communication in advance did not help). I have read that since 2019 the burden of proof is with the party who sends the invoice. So, how is something like this being handled by the Betreibungsamt in relation to the medical sector and bills from doctors?