"Free Month Mail" How does it work?

Hello dear Community,

sorry I have to bother you but EA doesn't give a .... about me since i'm currently not subscribed to SWTOR.

Anyways I got this E-Mail claiming to give away a free month of subscription status if I subscribe till 23.06.

So my question is do i have to have a real subscription or can I just buy a gamecard over two months and get the third for free?

Hope you guys can help me :D

Now have a nice day and may the force be with you

Ivarson