You should remove that number that you do not recognize.
Open Settings ➡️ Apple ID (Your Name at top) ➡️ Name, Phone Numbers, Email ➡️ Edit, then remove the phone number that you do not recognize.
The next thing is to remove that phone number from the trusted phone numbers list.
Open Settings ➡️ Apple ID (Your Name at Top) ➡️ Password & Security ➡️ Edit, then remove that phone number from the Trusted Phone Number list, if it appears there.
The next thing I recommend that you should do is to change your Apple ID passcode.
Open Settings ➡️ Apple ID (Your Name at top) ➡️ Password & Security ➡️ Change Password.
Axel F.