Have you heard of google? That's all I did to find the contact number.
https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/t4114/canada-child-benefit.html#P228_15384
The purpose of child benefit is to help parents with the high cost of raising children in Canada. If the parent and child are not in Canada they no longer need help paying for things like expensive childcare. It is best to suspend your payment versus being asked to pay back (with a penalty) any child benefit payments that you didn't qualify for.
https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/t4114/canada-child-benefit.html#P228_15384
The purpose of child benefit is to help parents with the high cost of raising children in Canada. If the parent and child are not in Canada they no longer need help paying for things like expensive childcare. It is best to suspend your payment versus being asked to pay back (with a penalty) any child benefit payments that you didn't qualify for.