Have had this sort of thing myself on a couple of occaisons. My course of action is 2 fold first of all tell the offenders to render their invoices in ENGLISH as we live in England secondly never deal with them again and go elsewhere.
Incidentally I was connected to the Plumbing Trade for some 40 years "Aberdeen" Don't mean a thing. But "Yorkshire Joints" do. It is a fitting for Copper tube that has an integral ring of solder.