I've had good luck when I submitted updates a couple years ago, though not quite the same as your situation. There is an apartment building on my street that is addressed weirdly. Every unit has their own street address/number, rather than one number for the whole building. Apple assigned only one number to that building, which threw everything off for the rest of the street. I submitted an update for every building that was numbered incorrectly, along with a link to Google Street View showing the building number on each of the buildings/units. They got it fixed pretty quickly.
They even emailed me back for clarification/confirmation. There used to be a "Follow Up by Email" toggle in Settings -> Maps -> Issue Reporting, but I see they've removed that so I wonder if they even follow up anymore.
If Google Street View has been updated since the business moved, maybe try showing them that and/or include a link to the business's website if they have one. Or if they keep ignoring your reports to fix the existing location, maybe try submitting an "Add to Maps" request for the new location and see what comes out of that.
