Think you rooted your phone using third party applications rather than flashing via odin huh..

trying these methods wont unroot...
to unroot you have to do certain procedure.
Use chainfire's triangle away to reset your binary coubter, which counts the number of custom roms you installed..

and still to regain your warranty.. you need to edit CSC.. its a bit risky and lengthy process.. there are many threads in xda for that.. search 4 it

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