Is your manager or HR department aware of the implied status law? Have you provided them proof of your original previous work permit (to perform security check) and proof that you applied to get a new one?
Find this information on CIC website and provide it to them. They actually need to see it. That helps to clear doubts or mistrust issues. Don't make them think that you doubt yourself or that you are a fraud.
Remain calm and speak with confidence as you present that information to HR.
So fight harder and hang onto that job opportunity!
Stay positive. You WP will arrive soon.
Thanks a lot for your suggestions, it's helpful. My situation is a little bit complication. My study permit expired on 3.31 and I applied for the pgwp on 3.19. My HR said because it is a change from sp to wp, I cannot work until the permit arrived. It's really weird, I got a email told me my application has been updated last evening, but when I log in to check what message it was, there is nothing new.
Cheers!