Not honoring promotion

I signed up for mobile, called and verified I was eligible. The promotion was for $10 a month for the first line for a year. I received my first credit per the offer and now I have a full price bill. I called xfinity and they said because of my internet, I don’t qualify. Each representative I spoke with stone walled me stating they don’t take any responsibility, will not honor, cannot get me to anyone that will. They offered the promotion for one additional month but it’s not even applied. It was the worse experiences with any customer service reps ever, I have never been so upset with any customer service. I definitely know I was lied to in order to start the mobile plan and then trapped me to be a customer. What an horrendous way to treat a loyal customer who has been with xfinity for over a decade. SHAMEFUL.