My internet is going slower than it should be?

I recently changed my internet from 1.5mbp/s to a 20mbp/s but in my area it will be shaped to 8mbp/s the only problem is its been a couple of weeks and my plan has definitly changed over but im only recieving 1.5mbp/s ive reset my belkin f5d8636-v4 and retyped my account details but it hasnt changed anything and ive turned off all firewalls and stopped all downloaded and done speed tests on speedtest.net but the internet still isnt going as fast as it should be. Ive called up my TPG internet company and theyre not sure what the problem is, if you could explain to me the problem and how i fix it would be much appreciated thanks