Being Overcharged for Years

I desperately need help.

I have been overcharged for years by Comcast.  When I called to inquire why my bill was so high, they said "oh, you're contract expired in 2022."

No warning.  No inquiry if I want to sign a new contract.  Just inflated charging.

When I called in June, the sales person very agreeably said she could issue a new contract and take my payment from $600 to $200.  Great.

Two months later and I'm still being charged $600.

I call billing.

"Oh, you need to contact loyalty."

I call loyalty.

"Oh you need to call billing."

I call billing.

"Let me transfer you to someone that can help you." 

I get transferred to scheduling a technician.

"You have a problem with your service?"

Another call...

You get the idea.

No one can help me and now i'm in the live chat who has basically ghosted me (I only see the three bubbles hovering).

I'm at my wits end.

Who can I escalate this to?