Refusal to payback money as per agreement

On 1 October 2013 we purchased a electricity saving device offered by Global Carbon. After many months of use we have not seen any savings. We got in touch with Global Carbon on multiple occasions to explain that we are not seeing any savings. We have kept all the receipts for prepaid electricity purchases made. After multiple requests someone came to my house to investigate. No results or answers, the person pressed a button now 2 lights on, another button 3 lights but no improvement. The people that came through are named Thinus and Evert. We still purchase the same amount of electricity for my prepaid meter. We told Pieter that we require our money back as the device does not work as we have not seen a single saving since the device has been installed. We are unable to get in touch with Mr Van Der Merwe as we are trying to get our money back as per the guarantee provided with the system. I have a list of calls made. First call was made on 06 Jan 2014 then May, June, September a multitude of calls in November. a Multitude of calls in February and March 2015. To date we are waiting on Mr Van der Merwe to phone us back to try and acknowledge our existence.