Order "confirmed" that I never ordered. Rental charges for returned modem.

11/25/2020 I received an email from Xfinity thanking and confirming my order for a speed increase. I did NOT order this. I immediately contacted them disputing this order and they did not respond. They are also continuing to charge me rental fees for a modem I returned in April (I purchased my own.) I have 2 mails confirming they received it. Despite chat, calls, and 2 letters, they do not respond.  They are just forcing me to file a complaint with the BBB to get this resolved.  This latest bogus charge is just disgraceful.