Firstly, please make sure that your new email address you provided is correct and existing.
Next, the reason may be that you have not activated your new account. In the email box, please open email from VietnamWorks, click the link to activate account before using.
Please note that you should also check All Mail, Spam Mail, Promotions (in Gmail) and Junk/Trash (in Yahoo Mail).
After checking, if you still cannot find activation email from VietnamWorks, please send email firstname.lastname@example.org to request us to change your username. We will help you activate it.