Ripped off

What do you do when your apple gift card for $350 that u got for a trade in has been charged $96.16 for a purchase that u didn’t make . And Apple support won’t tell me what the order was or who ordered it or where it was ship to And I only found out about this unauthorized purchase when I went into the Apple store to purchase a new iPhone . I’ve called support and I’ve. Been hung up on, I’ve been sent to every department And nobody seems to care and I’ve asked to speak to a supervisor . Yet nobody has called me back