Automatically receive the current billing cycle's data usage update from cellular providers at pre-determined frequency?
You can use the built-in Shortcuts app to automate actions on iPhone. It's not possible to completely automate the action of sending a text message, but you can have Shortcuts prompt you at a specific date/time and send the message with one tap.


From the Shortcuts app, create a new Personal Automation at your desired Time of Day.
Add a Message action to send a message with your text to a number of your choice.
Disable ‘Show When Run’ to run the shortcut immediately on trigger without opening the app.



When the time occurs, tap the notification to run the shortcut: