You can attempt to contact Immigrants, Refugees, and Citizenship Canada (the government agency in charge of eTAs) via a web form. From the IRCC web page:
What do I do if my application for an eTA is not approved right away?
While most eTAs are issued in minutes, some can take several days to process. In such cases, more information is needed before the application is approved. IRCC will contact you via email and advise you of the next steps.
Check the junk/spam mail folder of the email address you provided on your eTA application form. Some spam filters may block automated emails from IRCC.
The email from IRCC may include a request for:
- additional information or documents, or
- an in-person interview at the nearest Canadian visa office.
If you have not received an email confirmation with an application number within 72 hours of applying, you will need to fill out this Web form. To do so, you will need to:
- provide some basic personal details, and
- Under “Type of application” select “Electronic Travel Authorization”, then “Case Specific Enquiries”.
- Provide as many details as possible about the problem you encountered. It can take us several days to answer your inquiry.
It sounds like you've already corresponded with IRCC via e-mail (though check your spam folder to make triple-sure that you haven't received further correspondence from IRCC). Even so, the web form appears to be the "official" way to "ask about an application that has taken longer than the normal processing times", so I would try that if you haven't already.