If you need to call the CRA, you will need to know the following:

• Call only the phone numbers listed on their website. For individuals and families enquiries, you can call 1-800-959-8281 to speak with a CRA agent. They also have automated phone services. Please visit the CRA website for more information.
• CRA has a new telephone platform that offers self-serve options. When you call, you will now receive an estimated wait time to speak with an agent. You will then have the option to wait in the queue to speak with an agent, call back later or use one of the self-serve options available.
• At this time until April 30th, the CRA is offering extended evening and weekend hours for individual tax enquiries. CRA agents will be available on weekdays from 9am to 9pm local time and on Saturdays from 9am to 5pm except Easter weekend.
• The automated phone service is available 24 hours a day, 7 days a week.
• When you call the CRA, be prepared to provide your SIN, name, complete address, date of birth and details from your most recently assessed return, notice of assessment or reassessment to verify your identity.
  
  Source: https://www.canada.ca/en/services/taxes.html