I closed my account, but now abused by collections

After 16 years of being a Comcast customer for which I paid over $35,000 for TV and Internet service, I couldn't take the billing dishonesty anymore. So in June of 2021, I closed my account that had no outstanding charges. Several days later Comcast sent a bill for another $103, and ironically, proved my claim of dishonest billing practices. I did not pay the fraudulent bill. Now my Experian credit report shows a Major Derogatory on 8/31/2021 from SouthWest Credit Systems for the $103. I told them the account was closed and I did not owe the amount. Now on Experian, a second collection agency called Sunrise Credit Service has posted this year Major Derogatories on 5/05, 5/11, 5/18, and 5/24, all for the same $103. Yes, Experian is showing the same fraudulent debt reported by two separate agencies. Of course, I have entered a dispute. But this all started from a multi-billion dollar company that took over $35,000 from me, but now wants to abuse the system to collect a fraudulent $103. Brian Roberts is such a sad, loathsome, little man, isn't he.