Hello Guys and Compliments of the Season,
Please i have a website where people register for free and get free SMS(send free SMS to any user across the globe).

When you register, you get 5 free SMS units, then you'll have to purchase more SMS units after exhausting your free units.

Here's my problem, i have found out that some users are creating multiple accounts just to get more free SMS units.

So my question is: How do i stop this from happening?

i already check for duplicate email address and mobile number.

What else do i need to do to stop these type of users?

Thanks