Re: duplicate listings
you can't delete a listing - not even if it is a duplicate.
But you can report it as duplicate
If the duplicate is a duplicate of a listing you own and manage in your dashboard your best choice is contacting business support asking them to take down the dupe.
The best way to contact business support:
contactflow & request a call back
Talk to a specialist
Global Phone Support Hours:
You can request in many (maybe not all though) countries a call back of experts of business support by phone. This should be possible on official working days and during their the day time only - try it from 9 or 10 AM until 5 or 6 PM
Helmut Geissler, Google My Business Top Contributor | my G+ profile