Slowest internet

I have recently upgraded my adsl Internet line with telkom from a 2meg line to a 4meg line. In the last few weeks my Internet has slowed down so drastically, its not even getting close to 1meg. I've tried calling telkom customer service many times but I've just been put one hold for hours. i am sick and tired of trying to contact them to resolve this problem. I am paying for a 4meg line but my speed barely reaches 1meg. This is very disappointing and frustrating.