3 complaints later and still no resolution

In Jan we upgraded our line from 2 to 4mbps. Since then, we've only ever gotten a 2mbps speed. We've logged in excess of 3 complaints and 1 other hello peter complaint. 2 technicians have told us that our line was never upgraded to a 4mbps, but the sales and billing departments tell us that the line was upgraded. We tested a 4mbps Openweb line but also are only getting 2mbps. This tells me the fault is on the copper line to us. It seems to me everyone wants to pass the buck and nobody wants to sort out our problem.