The USPS tracking for a recent package of mine seemed to suggest that it had cleared customs but then it's status didn't change for a week. I initiated an international inquiry with USPS and magically the package started moving again the next day. USPS actually emailed me to say that it was up to customs and they couldn't do anything, but I suspect they did something.
https://www.usps.com/help/claims.htm. Click on the International tab to initiate an inquiry.