issue with inserting values into database in wordpress

Hey guys so I am trying to insert some strings into my wordpress database, it proceeds but nothing is sent over, no values are stored for some reason.

Here is the code:

$wpdb->query( $wpdb->prepare( 
    "
        INSERT INTO $wpdb->discount_info_guest
        ( firstname, lastname, email )
        VALUES ( %s, %s, %s )
    ", 
     $firstname, 
    $lastname, 
    $email 
) );
echo"working";
exit;

Let me know what you think, and if you need any other info.

Thanks!

Database:

Field   Type    Collation   Attributes  Null    Default Extra   
ID  bigint(60)      UNSIGNED    No      auto_increment  
firstname   varchar(60) utf8_general_ci     No  
email   varchar(60) utf8_general_ci     No
discount_code_used  varchar(60) utf8_general_ci     No  
order_state varchar(10) utf8_general_ci     No  1

    Indexes:  
Keyname Type    Cardinality 
    PRIMARY  PRIMARY     0