If your bill is overdue, carriers may suspend messaging services.
If none work, – they can see and remove carrier-side message blocks instantly. Apple cannot remove personal or carrier blocks. how to remove message blocking on iphone
If you are trying to text a non-iPhone user and it's failing, your phone might be trying to send it as an iMessage instead of a standard SMS. Go to Settings > Messages . If your bill is overdue, carriers may suspend
As a last resort, you can try resetting your iPhone to its default settings. This will erase all of your data, so make sure to back up your iPhone before doing so: If your bill is overdue