Full price for half speed. 20mbps Unlimited and get 11mbps

Why must i pay full price for half the speed? I queried this several times, the technician told me i have to see how it goes as i wont get much more than that? I please ask you to CANCEL this entire package as im not getting what we agreed on. I get no more than 11/12mbps and pay for 20mbps. Its not doing it for me.