How do I get this resolved?

I was promised by an agent that xfinity would pay off my remaining balance with Verizon if I switched over phone plans. So, I did, only to find out the next day that I was lied to. I've been given the runaround by multiple agents. Was promised a callback from a supervisor, only to get a call from someone telling me their supervisor is busy. Everyone has now told me there's nothing they can do. Im stuck with an over $1400 balance with Verizon, all because an xfinity agent tricked me into switching over, and the company is not willing to do anything about it.