Internet Problem

For the past 2 months I have been paying for 1000mbps download and 250mbps Upload.. but the speed i get is between 300 and 400 mbps. And this was just after I upgraded my service from 500 to 1000.. I am very unsatisfied with this service. I won't pay a single cent to them until they sorted it out. Doing tests but getting nowhere, they sent Metrofibre to my house and they said everything was fine on their side.. FIX THIS