No service notification

Hi, since I have had my new phone, when I am out of range of a signal I get a "No Service" notification.

That in itself is not too bad but it then sends another every 20 seconds or so until I am back in range.

I thought it was a phone setting but I cannot see anything and Samsung help say it is a  mobile service provider notification.

I cannot see it being a smarty setting myself but could it be?.

Never had this issue before so I'm convinced it's a phone setting.

Thanks for any advice.