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Unfortunately fitbits can only store between 5 and 7 days of data between sync so you will have lost data by now.
In order to get it syncing again I would try restarting your phone and then restarting your fitbit a few more times using this procedure:
https://help.fitbit.com/articles/en_US/Help_article/1186/
I know you have tried this already but give it a few more tries as it doesn't always work. If it still won't sync after that then there are some more ideas to try in this help file:
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