Direct TV sent my equipment bill to a collection agency

I turned in my equipment to an installer on moving day.  Direct TV had not sent  the box for me to send the equipment directly to them, even though I had requested it 6 weeks before my move.  I received a call from one of the ladies who bought our home saying that the box had finally arrived - I had already been in North Carolina for 10 days at that point.  Didn't think there would be an issue, until I get ambused by the Collection Agency!  I called my realtor, who was there with me the day we handed over the equipment to the installer.  She said she has the tracking #, but since it had been so long, she'll have to dig through her paperwork.  I'm curious as to why they didn't charge my Visa account - then I could have contested it.