AP approved, but not received, what to do

[lulx-co]

My AP was applied on Feb 11 at MSC. I haven't had any update from online message since then. However, when I called to inquire two weeks ago, I received a letter from NSC saying that my AP was filed at the wrong center, i.e., I filed at MSC, but it should have been filed at NSC. The letter says my AP was approved on March 18. If I haven't received it yet, I should call MSC. So I did, last week, talked with a representative, and was told that I should wait for 30 days to see if I receive the approval notice.

What else can I do to make sure that I can receive this AP before my international travel in early July?

Thanks for your help.