If it always had smoke from the exhaust and one oil change was overfilled, then the smoke is a different problem which needs to be found and fixed. To be clear, is the the gray-blue smoke of burning oil?
A slightly overfilled crankcase is no problem. A greatly overfilled crankcase can result in the crankshaft whipping the oil into a foam. Either the crankshaft and other parts can be damaged from hitting the oil, or the oil foam cannot be picked up by the oil pump and a lot of damage happens to oil lubricated parts in the engine.
How high was the overfill?
I'd make an appointment with the dealership you trust the most (or distrust the least) to have them check the smoke. Say nothing about the overfill. It's just about smoke, and demand a definite answer. The exhaust must be clear. If not, you're not meeting the emission laws, and you have a warranty that specifically covers this. You might contact Mazda Canada, 1-800-263-4680, and ask about the smoky exhaust and the emission control requirements. Again, don't mention the overfill. Keep things simple and to the point--the point being the improper smokey exhaust.
Every time you get your car back from service, every time, take a look at what they claim they did. Pull the oil dipstick and check that the oil looks new, clear as water, and the level is correct. If the oil is that clear, you might need to see the level by laying the horizontal dip stick on a paper towel to see where the oil is absorbed. Check the paperwork when you leave the car to be sure they describe the problem, not just list the service writer's guess about what the tech should do. Be sure the paperwork you get back describes the work they did. We get what we inspect, not what we expect. You don't need to be a mechanic to ask the service writer to show you and put their finger on the clean new part that supposedly was replaced or whatever else was done. The first and only time we took our CX9 to the local dealership for an oil change they failed to change the oil or filter. My wife drove the half hour home, I checked the dip stick, and the oil was a half quart low and dirty. I phoned them, spoke with the same service writer, he lied about things until I asked him to check the work order. No oil or filter had been charged to the job. He changed his tune.