Phone hacked

How do you Unclone a IPhone 8 ?

I bought a Device from a “friend”

that has Copied the phones Imei and the serial number! Idk what else but each account has been compromised and everything I write or text or anything in that case has been read Out loud from the people who live next door me in a apartment Complex They didn’t think I was listening to them So that’s how I Found out Who has committed Identity Theft on bank accounts and Applied for loans and using my emails and Facebook acting as me! How can I get my device secure?