Was it factory unlocked or was it a Rogers locked phone with a no-commitment price?
If it was factory unlocked apple can exchange it, if it was a rogers locked phone bought at the no-commitment price, you'll have to go through rogers to unlock it again.
Apple usually don't repair, but replace with refurb, they probably gave you a locked model, unlocked IP4's are usually not in stock, give apple a call on their service numbers.