Not correctly providing service paid for

For the past year i have been paying for a 4 mbps adsl line and only receiving 2mbps. After months of calls to telkom and resetting the port numerous times i still only received 2mbps. Since i was only receiving 2mbps i downgraded to a 2mbps line and now i only receive 1 mbps of that 2mbps line. Is it telkom policy to only deliver half of what is promised. I am very frustrated with telkoms service and at times cannot even load a webpage due to slow speeds.