non returned equipment fee FOR EQUIPMENT I RETURNED

Since this began, I have now spoken with 5 different people over a period of two months trying to take care of this situation. Each time I've been told something different. 

I canceled our tv service a few months a go and received a pre labeled box to return the equipment in. I packed all of the equipment up and dropped it off at the post office with no problems. About a month later I got an email saying we were being billed for "non returned equipment". I called customer service and was told to ignore the charge and  that they would take the automatic billing off the account. The next billing cycle there was another charge so I called back and was told this time I would need to go to the post office to retrieve the tracking number of the package. At this point, the post office didn't have record of the package because it they only keep track of it for a certain amount of time and it had been too long.  Called back and told them I couldn't  get the number and they said they were going to escalate the ticket. Didn't hear anything else about it until I got another email saying if I didn't pay that they would get a collection agency involved. Called yet again only to be told that I don't need to worry about it and if they were to send it to a collection agency it wouldn't be for at least another 3 months so I would have plenty of time and once again it was escalated. Not even two weeks later an actual collection agency called me directly. Last time calling I was told that they were going to escalate AGAIN and investigate. That was almost two weeks ago and no one has contacted me. 

So to sum all this up I've had 4 separate charges for non returned equipment, 2 escalations, collection agency has gotten involved, and no actual help. I have questions about how this even makes sense.

1-  During all of this, I asked if they could look up the number on the package that was sent to my house but was told there was no way for it to be looked up. How can you not track the number of the package that YOU sent me to see if YOU lost it?

2- If there were any issues with sending the package on the post offices' end they would have contacted me, so how is it that it just seemingly disappeared once it left there?

3- Why does it seem like "escalation" is doing absolutely nothing to help the situation?

I am DONE calling customer service over and over. I am DONE repeating the same thing over and over with NO progress or resolution. And I am especially DONE about worrying over how my credit will be affected for something I have NO control over. This absolutely should not have been dragged out for this amount of time.