Bad internet service even worse service from call centre

My internet has been slow for a week now. I pay for a 4mbps line but have been receiving less than 1mbps consistently, when I called their call centre yesterday I was met with an agent that told me that the low speeds could be due to the fact that I connect via WiFi,(needless to say I was shocked). I understand network errors but for an entire week? Please can we get to the bottom of this before you loose one more customer. The call centre agents name is Phinius Baloyi and his supervisor is Danny Monyani at the JHB call centre.