The info is insufficient to indicate an error was made - 回複：請教各位

The info is insufficient to indicate an error was made on your I-94, w/o H-1b expiration info being released.

Generally, your H-4 status should be granted the same length as the primary H-1b, which was not disclosed in your post.

If the H-1b status expires on 4/15 (which is the expiration on your H-4 I-94), there is no error on your I-94.

It is also true if the H-1b is renewing the status, while such petition has yet approved at the time of your admission. In situation like this, you need to file I-539 for EOS.

You may try your luck at POE.
http://blog.wenxuecity.com/blogview.php?date=200806&postID=23446
BTW, contacting USCIS won't help you any, save your time.

It may be considered an error on CBP side, when you're given a shorter period in H-4 status while H-1b has been authorized a longer period at the time of your admission.
The solution is CBP, see link above.