Cancelled Xfinity Internet & now I have to return a Flex Box?

I cancelled my Xfinity internet service over a week ago after switching to Sonic Fiber (soooo much better btw). While I was on the phone with the Xfinity rep to cancel my internet, they informed me that since I was using my own modem and router, I wouldn’t need to worry about returning equipment as there’s nothing to return. However, they later mentioned that they see there’s a flex box associated with my account that needed to be returned. I was confused because I never received such equipment from them, which I told the rep. I can tell that the rep was a little confused on how to handle the situation. He told me that it was a hypothetical situation and I might or might not be charged for it (he couldn’t see it on his end lol so is it there or is it not???). He just instructed me to contact Xfinity again if I get a notice or a charge regarding the said equipment. 

Sure enough a few days later, I receive a text and an email about returning equipment or else I’ll have to pay a fee. I’m not sure what to do about this because I never received the flex box. I’ve been using Xfinity for years ONLY for the Internet no matter how many times they tried to sell their mobile and other services to me. I’ve always declined everything. Now they’re saying the flex box which is a tv box associated with my account is bizarre. I don’t even have a tv. Please check my account and see there is no flex box or tv services activated on my account because I never received it!! I don’t want to be charged incorrectly for equipment I don’t have just because I decided to part ways with Xfinity for a better ISP.