Preventing Fraud?

[gab1982]

Hi I use modernbill and 2checkout is my credit card processor, recently i had alot of signups through 2checkout mostly they where from vietnam and in the past I noticed most fraudulent use came from there so blocked the country, however 3 of them got through my safety net, because there IP orriginated from the US, is there any system i can use which can prevent this from happening again? besides the use of a phone system, due to the fact some clients prefer for me not to call them due to different time zones and may use phone numbers which are incorect.