If you need to communicate any information to the City of Toronto property taxes department, call 311. They can help you with your property taxes problems. Sometimes if they are unable to help, they would give you another specific taxes department phone number to contact.
In my case, I called 311 and explained that I wanted my bank to pay my property taxes on my behalf through regular mortgage payments. I provided my bank branch information and location but not my bank account info, only the bank location information and bank name.
Then I called my bank mortgage department and let them know that I want the bank to pay for my property taxes through regular mortgage payments. Sometimes like you said, the bill will still come to you asking for payment for property taxes, in that case call your bank again, and they will be glad to adjust your bank mortgage payments amount to reflect the required changes.
Ask to speak to higher authority if your message is not getting through to your bank correctly. This problem should not be happening, and can be easily rectified through a call to your bank mortgage department.
If all of that doesn't work, then you might want to hold both your bank and City of Toronto responsible by going to CBC's news "Go Public" and telling your story of bad experience with them both. In a lot of cases, out of caution for earning a bad reputation, the bank and City of Toronto would both scramble to fix your problem right away, after it comes out in public news.