Client keeps disconnecting

Hello everyone, I have -as I recognized- a common issue with League Client, it's keeping me away from game and disconnects from chat every single time it is reconnecting to the chat. I've tried every single method suggested by Riot on their Connection Issues page and it didn't help at all. My internet connection is working good in every app expect League Client, even when I once run the LoL tutorial - it was not lagging. Every time when I try to find a game, it disconnects me after 1-3m like I didn't accept the ready check. Also I don't have a router, I am using just regular USB modem, so have it in mind, trying to find a solution. And of course, week ago everything was working fine as it should work.
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