Had similar experience trying to add a restaurant to Google Maps, our own even. First time, rejected because didn't exist, it did. Second time, they say they sent a letter, and they see that someone received it, no one did. We wait a month, they say they sent another letter, we wait another month. Nothing, and now they stopped replying too. Wait another month, suddenly the restauarant magically exists on Google Maps, with the wrong images, wrong address, wrong open times, but the pin is the right place at least, so I guess that's cool. Took another month or two to force through all the corrections too.

This was made 2-3 years ago, probably worse today. Absolutely horrific experience, and they have zero motivation to fix it, because people like us still want to be on Google Maps, especially if you're not in a super good location, so people can actually find you.

Another path may be to add the business to OpenStreetMap first; I get the impression that Google will scrape changes to OSM and add them to it's dataset. (I've seen several small changes I've made only to OSM get propagated to GMaps a few weeks later. Possibly it's a coincidence, but when the features are exactly the same shape as the ones I drew in OSM, I get suspicious.)