So then are we paying for a product that we cannot utilise?
If your exchange only supports 4Mb you will only be charged for 4Mbps (previously 2Mbps). So if you were on 4Mbps before you will get a discount of roughly R120 per month. If you were on 4Mbps before and your exchange now supports 10Mbps, you will get a free upgrade to something between 4 and 10Mbps depending on line quality.
Really nothing to complain about here...