Very painful service, I need my money back

I bought a taser stun gun from this company, the 1st order was delivered okay and all was good with it. The second order a week later came to my place of work, enclosed in their packaging was a damaged, second hand and faulty stun gun. I logged a complaint for them to collect it and replace with a new one, since I bought a new one, till today I dont recieve feedback. They keep saying they are investigating. What is to be investigated?