ISTORE SOLD ME A FAULTY IPHONE 8 NOW THEY WANT ME TO PAY FOR A NEW ONE! HELL NO!!!

I HAVE JUST BEEN ****** BY APPLE STORE(CENTURY CITY,CAPE TOWN) ! pls help me expose them!

I bought my son's iphone8 two months ago and two weeks back it stopped charging. We returned it to their store in Century City where we bought it and they sent it to their repair center. We waited for more than a week to get feedback and GUESS WHAT? they say the batt has punctured and they claim the fone has been tempered with and I must pay R8000 which is absolute nonsense! The consultant and the manager at the store saw it wasn't. They were adamant the phone will be replaced and now the say a warranty has been voided. If the phone was tempered with why did they open it? They have nothing to prove that we opened it except that they opened it themselves.They are a bunch of ******, ******** people by selling them phones with CHEAP BATTERIES!* I'm opening a case!*