How can i stop the fraud on my website?

I have an online website where users can browse and place an order online! But recently I have a feeling that since we have avail promo codes and other discounts, customers are abusing it! And I can also see that there are a lot of fraudulent transection are been made and also a lot of cancelled orders.

So if you guys know any plugins where I can identify and stop this would be great!!

You can block their ip address, name or cc. If this persists your payment processor can ban your account. I suggest you take action quickly.