Welcome to the Samsung Members Community Canada. Please follow the below steps on your phone and check:
Open Settings >> Apps >> click on three dot menu(Top right corner) >> Show system apps >> select Phone application>> click on Notifications >> click on Missed Call >> Enable/Alert Missed Call notification.
So... regardless if you have all the settings correct in each app to get the notifications, if you have the "Clean Master" App on your phone, when you go into it, check the settings on the "Notification Cleaner".
First.. find the "Clean Master" App under Apps in settings or you may see the little brush at the top of your phone.
Next.. click on "Open" at the bottom left, then you'll see the Notification Cleaner. Click on that icon and once it opens up, click on the Wheel in the top right hand corner, then click on Settings. Listed below are all the Apps and if they are green, the notifications are MUTED. Unfortunately all the ones in green are automatically muted... including the phone icon that would control Missed Call Notification. Once I flipped the switched off/the colour gray, we tested it and there was a number on the phone icon on my home screen to show I had 1 missed call. What a relief!!
Really hope my instructions are clear and this helps anyone with the same problem. I believe I mentioned before that I have a NOTE10 Plus. Have a great day. 🙂