Live Chat Agent Lies me and changed my internet Plan

Dear XFINITY service,

I am a new customer, who started to join Xfinity internet Last November with 75 Mbps plan of ~ 29.9$ per month, contract 1 year. I paid for December-March. An agent tried to convince me to join the mobile line to get more discount, I joined 3 mobile lines but no discount but the fee increased to 40$ in April. I contacted to live chat agent again, and they lied again and changed my plan to 400 Mbps with the same price as my formed deal (30$) + award of 100$ gift card. Now I have seen my next bill is 62$/month.

This is unacceptable. I would like to file a complaint for lying to a customer.

Thank you.