phone hacked trying to get person out

I have a desire HTC 526 that's been hacked. It has obvious signs but I cannot remove the files that are giving person access. This is my 6 rh phone and 3 carriers in 3 months of anyone has any idea how to block or remove please help. The phones all act as if rooted I'm asked for su permission when I try to remove files. I have tried su and nothing happens. I have had one time where king root looked like it took bit it only lasted minutes before telling me I was not rooted. Whoever this person is is consuming all my data in the first two days of cycle Verizon tells me my phone is using 5,go of data in less than a day when I'm not online and all of it is going to videos. Any suggestions would be appreciated

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