incorrect billing charge

Hi, I need assistance with an incorrect billing charge. I previously spoke with a live Xfinity support agent who explicitly promised and confirmed a rate of $50 per month, but my bill has now increased to $70. I am currently abroad and unable to call, and when I tried the chat function it always says "Looks like our agents aren’t available right now." I have the full chat transcript saved as evidence of the previous agreement. Could an official support employee please look into my account and help adjust this back to the promised rate?