Paying for a service and not receiving it

We have had a 10mb line for about a year now and have not received speeds even close to that. We have placed numerous calls to have this rectified with absolutely no help to the point. We finally then were told to move to a 4mb line and that that would correct our issue and give us a better connection. since moving we have had even worse speed to the point that we cannot even send emails or browse the internet. After placing even more calls to the support department we were given a fault reference and have yet to hear from them. Not a single consultant has ever gotten back to us after any call or log, not even floor managers. Absolutely appalling service and a complete breach of contract.