Hi Sun,
Sorry to hear about the troubles. Let's start by checking out the following Help article: https://www.bungie.net/en/Help/Article/11930
Have you tried calling your ISP to see if they have identified any issues on their end?
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Thanks for answering but We've tried to follow that article.It's seem doesn't work for us. and last month I've called them but they have no idea what happened because other game is just fine :/