Have you written to them about the matter ? You might then wish to escalate it to the Renter's Association (
MV Zurich ) - they charge a consulting fee ( cheaper in the long term were you to join them as a member ). Best to have photographs / videos with date and time stamps imprinted to show the MV.
Adresse:
Mieterinnen- und Mieterverband Zürich
Tellstr. 31
Postfach 1949
8026 Zürich
E-Mail: info(at)mvzh.ch
(Keine Rechtsberatung über E-Mail)
Öffnungszeiten Sekretariat:
Mo–Fr 9–12 und 13.30–17h
Telefon: 044 296 90 20
Fax: 044 296 90 26