Need to know how to file a complaint

I moved and had Xfinity change my address, I was told I would not notice any changes to my service for address change but the next day my TV were not working; so i was on the phone with Xfinity for a while to get corrected.  then i went to a store for a phone upgrade and was there for hours i purchased the 16 pro but when they tried transferring data they realized they sold me wrong phone (128GB) - since I was having issues with transfer they had me keep both 16 pro (128GB) since my phone # was active but also keep my old phone since data didn't transfer over - they ordered new phone (256GB) 6/14 but as of today 6/20 issue with shipping and phone went back to sender (Xfinity) - I went back to store today to return my phone & just have my old (reliable) phone reactivated - then i asked to have accessories returned and they wouldn't n my screen protector (which the store put on the wrong phone) - so i am very unhappy with the service and getting [Edited: "Language"] on purchases when i was sold the wrong phone - this whole process with Xfinity for internet, cable & mobile was horrible - plus i am out over $100 on the accessories since they would not give me full price refund plus would not even refund the protector