Hefty Bill on Telus Internet though it is disconnected 6 months back

Hi , 

I have disconnected my Telus connection 6 months back and i am not using it from past 6 months back. 
No body responded to me on the customer service for the proper disconnection rituals. 
Hence i just stopped using it and returned the equipment. 
But still Telus is sending me emails and messages about i have a due of 2553.71 CAD . There is no justification for this bill also. 

I have visited multiple Telus stores in Ontario and everybody said they cannot resolve the issue. 

Asking a question in the forum is the final resort or approach i am taking. As far as i know i have paid all my bills as per my usage. If Telus is not able to track the customers that is not my problem.

They said me voice message to call on a particular number ( attached screenshot) if i call nobody will respond . Some weird voice help options will come and thats it the call doesn't go through. Customer service is more than pathetic.

I am attaching the required screenshots for the reference .