Here's the link to the warranty checker and from there you can also create an RMA:
https://myapps.taec.toshiba.com/myapps/admin/jsp/webrma/addRequest1NoLogin.jsp
Note that the serial# shown in SMART is not complete as is the case for many other brand sof HDDs.
For example a 2TB Toshiba shows the following Serial Number in SMART:
Device Model:........