My galaxy s20 has begun to randomly play the over the horizon ringtone at all times of the day 24,/7
It's not even the ringtone I have set for calls. I have to restart my phone to stop it.
I am so sorry to hear that, and can understand how annoying and intrusive it can be to have unwanted sounds randomly coming out of your phone. If your phone or tablet is misbehaving, it's possible that a third-party app is causing the issue. To figure out what app is acting funny, you can use the Safe mode feature. In Safe mode, your device won't run any third-party apps. This allows you to easily identify and remove the app that may be causing the problem. Give this article a look: https://www.samsung.com/us/support/answer/ANS00062983/
If it isn't a third-party application causing this, you can try a factory reset. Please bear in mind you will lose all files you have not backed up, so do that through a cloud service or physical medium (i.e. computer file transfer or Smart Switch) before attempting this: https://www.samsung.com/us/support/answer/ANS00062029/
Lastly if those two do not help, your S20 may need to be evaluated and potentially re-flashed. You can view your options here, the most popular being walk-in service locations: https://samsung.com/us/support/service