How can I get my promotion change from gigabit extra to gigabit and keep the promotion agent said that I couldn't and it would cost me

Just talked to an agent to decrease my internet speed from gigabit extra to gigabit I am on a promotion and had a check out about 30 minutes ago and was told that my hardware my laptop is only able to handle up to a gigabit connection and they have me locked into a 1.2 or 1200 megs plan and I want to reduce it and they tell me I can't and if I do my cable box I will have to pay for and it will cost me an additional $30 a month at least on top of what I'm already paying which is around $180 for everything how can I get this situated cuz I'm about ready just to drop service completely