3 Months worth of 2mb for the price of 4mb

Since December 2015 I have had issues with our company DSL line. We are currently paying for a 4mb line and prior to December we were syncing at 4mb on the router and getting around 3.5mb on [URL Removed] which is fine and I understand that overhead takes .5mb. Since then we have had the line sync at 2.5mb and Telkoms call centre tells me that is 100% correct and thats what 4mb means in the world of Telkom. ? have worked in Telecoms for more than 12 years, so I know this to be false. I will not accept that I am paying for a service that I am not getting. [URL Removed] That is the speed I am getting. Which is even lower than 2.5mb We are running a business on this line with 8 staff members needing to access the internet to service financial based clients. This in turn affects my clients which hold the company accountable. So I will be holding Telkom accountable.