If you still have your old mobile banking app and can log into it,you can actually change your phone number in Settings (if you also changed sim-card,that is).
Yeah, in what universe? I can bet you any sum, that most expats living here long term doesn't leave the country 10 times, not even close to that number.
Maybe you shouldn't listen to people.Loads of them are not doing it the correct way, and sometimes it's just a simple solution like changing browser. Or, maybe they don't understand the window when you can submit the 90-days report online. It's not rocket science.