Complete Recovery Corporation Email

I recently canceled my service over the phone and the customer service representative asked if I'd be returning a flex TV box I had several years ago. I explained that I have lost the box and he said no problem and that he'd remove it from my account then proceeded to cancel my service. Now I am receiving texts from Xfinity and emails from a sender called Complete Recovery Corporation asking me to return the box. I already told the representative I don't have the box, so I don't know what else I am supposed to do from here. I don't want to contact this third party company as I do not know if they're a real company or a scam. I also do not want the outstanding equipment return to go to collections or something, as I would have paid a lost equipment fee if the representative told me to when I told him I no longer have it. How do I make sure this gets removed from my account and doesn't go to collections?