I currently have a Samsung Galaxy A50 that I've had for almost 3 years. Recently it has gotten an interesting problem where the alarm cannot be turned off except from the Clock app. It is very annoying that the cross button doesn't appear at all and the alarm doesn't even appear in the notification panel when it's ringing. I have to unlock my phone then navigate to the clock app and manually toggle the ringing alarm off. Only then will it stop. Sometimes it doesn't ring at all. And yes, I have tried shutting off my device. I really hope that there would be an easy way to solve this so I wouldn't have to buy a new phone. Also this doesn't really suit with Samsung's image and brand.
@Tomska37: That's a strange one. Please can you try heading to Settings > Apps > Clock > Notifications > On, and toggle on each of the subcategories, especially 'Alarm and timer alerts'. To further troubleshoot the issue, please try pressing the Power/Side Key next time your alarm goes off to see if you're able to switch it off in this manner. It may also be worth heading to the Clock app > Alarm > Press and hold on your current alarm > Delete all, then tap the '+' symbol and set it back up again. Furthermore, press and hold on an empty area of your Home Screen > Widgets > Clock > Alarm > Add, for ease of access to your alarm.