Incorrect Billing after a number of quotations

Another phone call to pay our account after us disputing the fact that we were quoted incorrectly for our internet service from Telkom. This after we wanted a line upgrade we called telkom business and app**** - the consultants quoted us around 3k per month and then we were invoiced around 10k. This is now three months since we logged a dispute and have visited telkom Menlyn mall as well as spoken to many telkom representatives telepathically and still Telkom insists we pay the 10k or we will lose our internet service. At least three official disputes have been logged and nothing has been done to resolve this... On top of all this drama, the internet speed etc is not even close to what it should be (which is another long story and disputes have been logged) but, we upgraded from 10mbps to 40mbps but got 10mbps then to 20mbps and got around 6mbps and again to 10mbps - its a mess - we are not getting the speed we pay for and we are shaped when we are supposed to be unshapped... This is utterly unacceptable. Where a service provider forces the client who pays for services into a corner. So, the crux is - we are not even getting what we pay for and we are being charged incorrectly.