@engineer,
Thank you! I just contacted them. But when I think about it again, everything is still so ridiculous. I am an international student from China. In China my accounts occasionally were suspended too. But in China at least i knew my account was suspended because I said something bad about/disagreed with the Communist Party! And now the suspension here really surprises me and I myself can't even think of a possible reason why. I can't believe in China many people around me said US has little censorships. I am still so angry and I hope they will tell me they made a terrible mistake.