That's interesting.  I mean if the $30 off can be applied twice, sure you will be benefited.  

Amazon.com used to have this $30 off only applied to the NEXT purchase.  But I just checked their site and it's said you can use it on the first purchase.  I think the email that sent to you contains wrong message. 

You can check your Chase Amazon.com credit card statement to see if the $30 has already been taken off as a credit.  Or, you can give them a call to verify.  It seems to me that the $30 off can be used only once.