who can i take my galaxy s5 to if i want it checked for root accessand can it be unrooted?

my neighbor has control of my phone ,listens to all my calls ,gets all my texts and prevents me from downloading apps, as soon as i download an app it is FORCE STOPPED. she has had physical possession of my phone at one time,im not computer smart and it driving me crazy, att wont help and samsung wont help either since the warranty is somehow void. is there any possible way toget my phones back to factory? wheni factory reset it seems it resets to whatever they have installed on my phone.PLEASE HELP.

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