A deep dive into DIN 53507 PDF!
Politely inform them that the standard has been withdrawn and replaced by ISO 34-1 (or DIN ISO 34-1). Offer to test according to the current standard and note the equivalence in your test report. din 53507 pdf
The replacement standard is (Rubber, vulcanized or thermoplastic — Determination of tear strength — Part 1: Trouser, angle and crescent test pieces). A deep dive into DIN 53507 PDF