Line Syncing Slow

Up until a few days ago my Internet was working fine. I pay for a 4 mbs line but today i ran some tests and found my line is syncing at 2mbs. I spoke to Iburst and they logged a ticket which was just closed an nothing done about it. They explained that you guys at Telkom did nothing. I really would like to get what i pay for. I also understand that the line wont sync at exactly 4mbs but it was certainly faster than 2mbs a few days ago. Appalling service from a terrible company.