How can I speak to a manager or supervisor???

A few weeks ago I went in to a xfinity store to add 2 wireless tv boxes. To my surprise when I got home I realized I was given wired boxes. After speaking to customer service and several failed attempts to activate the boxes on my end the rep activated the boxes on their side. And scheduled a service call for a technician to come out. The technician came and refused to run the lines to the rooms I wished to add and advised me to call tech support and “order” the wireless boxes as he said they do not carry wireless boxes with them. After numerous attempts to order the wireless boxes, tech support refused to ship them to me and said I needed to go back to the store to pick them up myself but said I should call ahead to make sure they have them in stock and gave me a number to call. Unfortunately that number was the general xfinity number back to tech support as you cannot call a local xfinity store. So I head back to the store and as expected they are out of stock. The representative I spoke to took the two wired boxes from me and said he would credit me for them, and would ship me out 1 wireless tv box (as I decided not to go with 2) and waive the s&h charge. A week later I received the box and was able to set it up myself. 
Then the bill comes…. Not only did the rep at the store not credit me for the 2 wired boxes I never got service on.  I was charged for 3 new tv boxes + a partial charge for adding a tv box + $15 for shipping and handling for the wireless box. 
I have called and chatted to several people to resolve this but somehow I keep getting people who cannot comprehend what Xfinity has done wrong here. I’m at my wits end and if I didn’t go through enough trouble and weeks of issues adding a single room to my account I refuse to pay more then I owe for these services. I’m ready to cancel if I can’t get this resolved.