Bad service.

I bought my phone at sterns on 6 of march 2021, February it had a little crack, then on the 16th of June the phone went blank and funny we two with my sibling who bought the very same phone in the same store and his one isn't cracked but on the very same day his one also went blank as mine!! I'm assuming it is under warranty as I take it to sterns where they booked it to vodacom that tells me phone will be at the cost of 1700??? how the hell when the fault wasn't the crack!! I don't want them fixing my crack but to have my phone working!!!