Old account paid full now in collections

I am a current Telus customer in good standing from a bill perspective.  A few months ago I received an email from someone from  ....fstccs.com stating that I owed 78.40 from a account I had 6 years ago.  We pay our bills in full.  I call a Telus agent and was told it was an error, don't worry about.  Fast forward, I received emails from a collections agency regarding the same account.  .....actioncollections.com.  Again explained the situation, no bill forthcoming, just threats and demands.  Went back to the Telus agent again and "Alberto"(very helpful) stated again that yes he sees the flag, leaves the call for 20 minutes, comes back and says the bill is 0 and everything is ok.  The problem is that this is the same response I had several months ago which I took a transcript of.   Perhaps send a message to the people who have collect bad debts for you.  If the bill exists, I will pay it gladly.  I have told at least 3 people in your organization that as well as the two agencies you hire.  However we have a business system where our bills are paid on time and accounted for so I know that it is not possible and this is supported by my repeated calls to your agents.

Can you please look into this further to ensure that this badgering stops?