Hello,
This is a known issue.
You have to send a request to the customer support explaining that you didn't receive this first payment bonus (mount etc.). Give them some information about your payment method and date/time.
http://support.my.com/games/kbPage/3/
If you have no answer after 3 or 4 working days, please, get in touch with a Community Manager (Mhuldoon, Fayne, Reira, Drakdish), by private message on the forum, with your ticket ID and the subject of your request.
Regards.