why is my package held by U.S. Customs and returned to me twice?

I have sent a package twice since June to my family in China which includes necklace, health product, clothing, food, handbags and the total weight is about 18 pounds. I have no idea why it has been held by U.S. customs twice and returned to me , the similar package I have sent more than 20 times via USPS, none of them has problem, is there anybody who can explain to me the reason and tell me what to do now, I have paid the postage by PAYPAL and how can I get my refund of postage for two times!!!