Unknown balance

I canceled my old account at the beginning of this year. And I confirmed with Telus many times about the account cancellation. They told me that I don’t need to worries it, nothing need to pay after I cancel it. Now after 6 months, I checked my junk mails, I found that the general credit services send me many emails about owe balance. They said that my account has owe balance around 106, and it will hit my credit score. Then I called telus, they told me they don’t know, I need call the GCS agency by myself. I use telus more than 8 years, never miss any payments. And now you just throw my account and never notice me anything in half year.