Lied to repeatedly about getting a credit for unused mobile and never got a credit

I was misled about xfinity mobile being a partnership with Verizon and I signed up for xfinity mobile - not intending to cancel my verizon service.  I was never sent sim cards and consequently, I never activated the service.  I didn't realize I was getting billed until after 8 months.  I was promised four different times that I would receive a credit for $877.  Then I received a message that my case was closed but I never got a credit.  When I called about the credit, the manager told me that it was denied - despite being told by multiple representatives that I was getting a credit.  I have 3 xfinity business accounts and one home with xfinity internet.  Even when I told the manager that I am going to cancel all of my accounts, he said that it was my fault and xfinity will not issue a credit.   Xfinity is dishonest and they should be ashamed of their conduct.  This is a scam.  I would appreciate any information regarding how I can escalate my grievance and potentially pursue legal action.