Messages are being sent which I am not aware from the I phone leading to deduction of balance

Check the following:

1. Settings
2. Phone
3. Click the third line (free translated) "Answer with text message"
4. 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.

Use this apple self help tool to de-register your phone number from iMessage. At that point Imessage will still work with an email address. But you can't have it both ways, the problem you are encountering is that other phones ask the apple server if you are reachable by iMessage and if you are thats how the messages are routed.

You didn't ask, but you shouldn't need WIFI for iMessage to work correctly. If it does not then likely you have changed carriers and kept the same number. If that is the case, log out of iMessage on all devices, de-register the number with the above tool, and then re-log in, letting your number get registered.