Unusual iMessage received from my mom, who wasn't aware she sent it
Check the following:


Settings
Phone
Click the third line (free translated) "Answer with text message"
The exact text you received is right there.


If you have a running phone call, your screen will turn black once the sensor will notice the darkness of your face being close to it.

Once you click on your phone during an incoming call, you can decline the call and answer with one of the messages explained above.

This has nothing to do with spying and hacking.