So I’ve had an iPhone for nearly two years now and I’ve lived that long with double notifications on every single text. It’s always been annoying, but I guess never enough to do anything about it. Apparently it’s a system default to repeat the notification.
Alas it’s a new day and for the first time, I ventured into settings to do something about it. To turn off double notifications on your iPhone, choose Settings, then Notifications, then Messages. Scroll to the bottom and find Repeat Alerts. Click on that and choose never. Or maybe for fun change it to ten.