Re: SMS messages ... may be ... redirected,
"getting the network operator to transfer your number to a new sim "
The fact that your phone has stopped working is a bit of a giveaway, though.
Plus the network will send SMSs to your phone warning you that the SIM will stop working soon - at least O2 does, I assume the others do similar things.
If you can get physical access to the phone for a little while, using Pushbullet or Continuity to echo the SMS to a computer would be easier, and the target would be none the wiser.