How does Turbo tax know my return was received by CRA?

[beagles1st]

I have sent my first return the beginning of Feb (by mail), but I haven't got any response from CRA yet. I also called and asked the agent at CRA to check my return status, but she said she doesn't have (access to) any information on my return and even cannot confirm whether they already received my file or not. So, I tried to submit Netfile and Turbo tax showed 'Message from CRA: The Canada Revenue Agency's record indicates that your 2017 tax return was already received'. How does it happen and why the CRA agent cannot see any information even Turbo tax can get this information? Is my return being processed?

[TurboTaxTanya]

Do you have a CRA My Account?
You can check the status of your return through this service.

Here is the link for how to set one up:

https://www.canada.ca/en/revenue-agency/services/e-services/e-services-individuals/account-individua...

[TurboTax-Dhiv]

You can only file your income tax return once, if you've already mailed your taxes you will need to wait for the CRA to process it.  Continue to follow up with the CRA.