how do you stop the 'google verification' calls about your listing?

Real verification is something you start yourself from inside your Business Profile, so any call you didn't ask for about "verifying your listing" is safe to hang up on. And never read out a code Google sends you to anyone on the phone, that's how these people take over profiles.

Those aren't Google. They're sales calls or scams dressed up as Google, which doesn't cold call businesses to say your listing will be removed. You can't really stop them, only cut them down. Don't press any numbers, that just confirms the line is live and you get more. Turn on your carrier's spam filtering, block each number, and if you have a front desk tell whoever answers to hang up on anything that opens with "Google listing".