Terrible internet speed!

I pay for a 2mgbt line. Surely the fact my internet runs at 0.5mgbt is a breach of my contract. I am paying for a service I am not receiving. On phoning the call centre I am informed it is slow due to the exchange and there is nothing that can be done to fix it. When I ask if the exchange is due to be upgraded/repaired I am informed by the call centre that no, nothing will be done, there is no plan to do anything about the exchange. I know I am not the only person in my area experiencing this problem. I also asked the call centre where I could report this and how I could get someone to give our area attention. I was informed there is no one to report to and no one who can do anything. I am really frustrated as I run a bussines from home and the slow internet is affecting it. Surely there is some legal action that could be taken. I am at my wits end.