Joke Collection Website - Public benefit messages - My Apple 5S has been sold, but the buyer has been receiving short messages from others, and the APPLE ID has been logged out, but it still doesn't work. What should I do?

My Apple 5S has been sold, but the buyer has been receiving short messages from others, and the APPLE ID has been logged out, but it still doesn't work. What should I do?

Reasons for receiving SMS: I may have used iMessage before, and I didn't have the right to log off iMessage when I logged off, so now users can receive SMS sent through iMessage;

Reason for receiving the email: The settings of the email in the settings have not been deleted.