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Couldn't do it through the portal or phone. The "effective date" my marital status was "single" was on Dec 31, 2016. As my marriage was BEFORE this date, I couldn't update it. This CRA website is a joke.

And then the agent said I have to write and mail a letter to the Sudbury Tax Centre, and there is no way he could update my status on the phone (or through email). It's pathetic.
I have the same issue. Only beacsue of thsi reason my child benefits got rejected. So what did you do to correct the marraige date?