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Which part exactly does it say document invalid?

Did you have your own myCIC account when you applied or did agent do everything? In any event check the account for any letter of cancellation.

You can also try calling the Canadian IRCC number there is a roundabout way of doing it so google around.
 
Obviously something caused the cancellation. The GCMS notes will give you the real reason and you can then take steps to address it.

If everything was legit and you're the victim of a mistake, then you should be able to get a new visa. You should contact your school and ask them for help as well - the immigration department at your school has probably faced such cases before and can help you.

I personally know of cases where the school defers admission to the next semester or allows students to join mid-semester and take catch-up classes (both happened at my business school).

Don't get too stressed. If you're a legit student and all your papers were in order, you will be able to sort things out soon. These things happen sometimes.
 
Which part exactly does it say document invalid?

Did you have your own myCIC account when you applied or did agent do everything? In any event check the account for any letter of cancellation.

You can also try calling the Canadian IRCC number there is a roundabout way of doing it so google around.
On the CIC account page, the new message reads as “document invalid” that’s it, nothing else

No letter as I am sure I would have been notified if something came up as both the times when the visa and passport was issued I got the response on my email address