There could be instances where a client of yours has more than one listing in Google My Business. Google and people in the forums suggest you keep the best (optimized) listing with the most reviews, and delete the others. Now, removing the other listings may work up to a point. You need to take ownership of all listings, but it takes time for the verification postcard to arrive and it may not solve the issue. There are cases where the deleted listings popped up after a few months with no reviews attached to them. Only Google support can merge listings. Contact Google support: Talk to a specialist, Leave a message at their Facebook page. There is an option to use Messenger or use the Find Support page. Reach them on Twitter. Use the support option from within the GMB (left menu). Then you will have the option to request callback, chat or send an email. A person from GMB community will probably respond and ask for the GMB URLs for all the listings so they can forward the issue to the support team and they will merge the listings and the reviews.