security measures during checkout??

hey guys so i sell xbox live memberships as you can probably tell by my username. had loads of issues with chargebacks because i was using paypal. now i am using my own dedicated merchant account and i am seeing that there are still fraudulant orders coming through so i am waiting on more chargebacks.

So therefore to carry on i need to do some security checks whilst the user is going through checkout as the codes are automatically sent on the invoice. what options do i have?

The only one i can think of is telephone verification but other than that i am clueless on what i can do. so any suggestions and also if someone can point me in the right direction of a suitable telphone verification system that is easy to implement on zen would be great guys

cheers

What do your competitors do?

one company openly admits on there main page that they do telephone number verification. another one did not reveal what they do but when i phoned them they simply said they do alot of internal security checks. it is all automated though as they give instant delivery like myself. im just a one man company at the moment but wold like that to change shortly. :lookaroun