Preview Xbox

The 360 preview and Xbox One preview are two totally different previews, you'd need to be invited to the Xbox One preview and then wait to see if you're accepted.

As a side note, if you cannot access the preview forums be aware that you must enrol your xbox into the latest preview even if you were previously enrolled into the earlier previews, if you launch the Xbox Preview dashboard app, select the registration option
and enrol for the latest xbox experience preview then once the Xbox is enrolled you should be able to access the preview forums.

As a side note, if you cannot access the preview forums be aware that you must enrol your xbox into the latest preview even if you were previously enrolled into the earlier previews, if you launch the Xbox Preview dashboard app, select the registration option
and enrol for the latest xbox experience preview then once the Xbox is enrolled you should be able to access the preview forums.

support.xbox.com/.../xbox-update-preview-faq

Check out the faqs and please post any issues you have as a preview member to the preview forums. We can not help you with preview related problems here due to the restrictions in the preview tos. Good luck.

The 360 preview is not the same as the xbox one preview.

You can not be invited by someone already in the preview program on the 360.

Support have given you the wrong information or just got confused with the xbox one preview.

Either way,you will not get in the 360 preview program.