Telus taking me to collections after an account closure from 5 years ago

cont..

Today the person from the loyalty team called me and stated that the reason for the account being reopened was due to an equipment not being returned and that I would need to provide them with the tracking number that I was given for the returned device. This was 5 years ago of no communication to me about this whatsoever so logically I do not have that tracking number any more. I informed to the agent that because it was a 5 year old return that I wouldn't have the tracking number anymore. They informed me that I would need to call Canada Post and give them my account number and they would be able to provide me with the tracking number that was used. They then informed me that they would call me later this evening to check up on the issue. 

Shortly after this call I called Canada Post and they mentioned that since this is a 5 year old return that they will have achieved it and that Telus would have to be the ones to phone and speak with Canada Post's commercial department and see if they can get the tracking number. 

The collections agency that has been emailing me has already put a negative impact on my credit score for this. I have been a Telus mobility customer for 10+ years and a home services customer for 5+ years. It's shocking to me that this is how they handle loyal customers. I also have not received that call this evening as promised. 

What are my next steps here because I know I sent the device to be returned as it is not here and I wasn't even a Telus customer for some 2020?