Not Receiving what I pay for.Poor internet service

I have been paying for a 4mgb line and for the past 2 months I have slow internet speed and my average download speed is 2.4 and upload speed is 0.6. After 5 pm till about 1am I can't even get into some websites and I usually have to use my 3G MTN stick to get on the internet. This is getting very frustrating. I mainly use facebook and Sars efiling website. I have phoned Telkom to help me and then my internet is fine for a day or 2 and then it starts again. In the passed I would phoned in for technical support but now there is no after hour support at Telkom after 5pm. Its very frustrating because I'm self-employed and my computer and internet is my bread and butter.