Promo discount was not applied

On 4/14/2023 I signed up for internet and the phone line with device with Xfinity at 3630 Factoria Blvd SE, Bellevue, WA 98006. On 4/15/2023 I came back to transfer one more line and get another device for my child (iPhone 13th) because <EDIT: Removed Personal Information> told me about the promo, if I would transfer another line I would get 500$ off for device. So, I decided to make a gift for a kid. I came back to the store a little bit later because my bill was higher than supposed to be. <EDIT: Removed Personal Information> told me that Xfinity will adjust the bill next month. It did not happened. I came back again and <EDIT: Removed Personal Information> opened the ticket with my issue, told me to come back in a month. I came back in a month, <EDIT: Removed Personal Information> was no longer an employee, so I talked to <EDIT: Removed Personal Information>. He looked in my account and told me that phone number transfer did not go thru, that was why I did not get a promo discount. He opened a ticket again. I came back in a week and I was told there was nothing they could help me with. Not sure what happened, either the employee <EDIT: Removed Personal Information> made a mistake or system got a glitch during the phone line transfer, but I signed up for a device and a phone line for the kid because of this promo. None of this is my fault but now I pay the full price for the device. IFor the past couple of weeks I've been trying to find an email or address to complaint about this situation with no luck. I hope someone will provide the contact information so I can file a complaint. Thank you