Send a text message from a strange number to confirm the shutdown.

The other party blacklisted your number.

Blacklist setting method

First, find the Phone icon on the iPhone home screen, and then click Open, as shown.

2. Take the phone number in recent calls as an example, click the "Recent Calls" option at the bottom of the screen, and then click the "exclamation mark" icon to the right of the phone number to be blacklisted, as shown in the figure.

3. In the phone number profile, slide your finger up on the screen, find the "Block this calling number" option at the bottom, and then click Add, as shown in the figure.

4. Then the system will prompt us to block the phone number, information and FaceTime, and click "Block Contact" to confirm the blocking, as shown in the figure.