Ardupilot flip on take off

I’ve been trying to configure my drone for ages.
At first, I did the worst thing you can do, switch + and - on the power module. I’m stupid, I know, it won’t happen again.
Since now, I’ve changed all the components except the chassis, of course. And I’m getting the same issue for some months: When the drone gets powered on, it flips on one side. I’ve calibrated ESC, reflashed firmware, calibrated ACC, GPS, radio, I don’t remember how many times, but lots of them.
By looking at the Mission Planner’s configure screen all channels seem ok, the radio’s screen shows the channels correctly. They are well hooked up. I’ve tried everything. I’ve even tied a rock to the opposite side of the drone and it still flips. By looking at Tower in my Android device, with telemetry, the acc seems ok, it’s flat, so I believe it’s not bad callibrated.
I am really desperated, the only thing that comes to my mind now is changing my APM to something like a Pixhauk but they are like 60 bucks, and I am afraid that if I buy it and it doesn’t work I may be wasting money, any suggestions???
Really thank you in advance

This is usually a matter of the wrong motor order and/or prop direction. Are you using Motor Test in Mission Planner to determine if it’s correct?