@asadabbaspaki
At the moment, I'm having difficulty confirming where the option is, but you need to go to http://selfserve.publicmobile.ca and find the option to report a lost / stolen phone.
In the same area, you can request (if you need it) a new SIM card for when you reativate your service.
Self Serve is spinning it's wheels for me at the moment, so I hope this helps.
