Unroot Device

A

AC Question

My phone just recently froze and I have been unable to turn it on since. I spoke with someone from Samsung and what they said was that there is rooted software on my phone. I'm trying to figure out why and how this has happened and is there a way to undo it?
So what happened. My phone rang, but it was in the other room, so I missed the call. I picked up my phone to unlock it but it froze halfway between the lock and home screen.
Phone will no longer turn all the way on. It just keeps flashing at the Galaxy Note II (yes, old phone, I know) screen. I can't get to the mode where I can factory reset (volume up, power and home) I was able to get to a DL screen which said:
ODIN MODE
Custom Binary Download: Yes (9 counts)
Current Binary: Samsung Official
Status: Official
The Samsung Agent said it means that my phone is rooted from some app I downloaded. I don't live near a Best Buy and the price just to put the regular software back on is ridiculous because apparently the do repairs that you don't even ask for.
Please can anyone help me?