Sent to Collections for Returned Equipment [Edited]

I recently canceled my services with Xfinity and switched to AT&T and it was the best decision ever! Xfinity was charging me $180 a month for just internet and AT&T offered me even better internet for $40 a month. When I tried to call Xfinity to cancel my services they hung up on me 5 times and then they still charged me for another month. I went into the store to cancel in person and return all my equipment only to receive a letter a few weeks later from them saying I need to return the equipment or I will be charged for it. I explained to them that I already returned the equipment and I didn't hear from them again. Then I get a call saying that it went to collections for the equipment that wasn't returned. [Edited: "Inflammatory"] I am furious and will be disputing all of this.