Wtf I won 7 and lose 3 and I have been promoted to bronze 1

I am a silver 4 player last season. My games in the rank are pretty good. I enjoyed it and got the first 5 matches all won. than, riot put me in bronze one. Can anyone in riot tell me what happened in the rank system? Or riot just want to troll me and let me start from bronze again? Please explain.
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