Replacement

I took my iPhone in for hardware fault. They told me they will replace it within 5-10 working days. Got message stating that they are replacing it but the are waiting for stock that will only arrive 4 or 5 June. When I asked them if they are replacing my phone they said yes but they can't guarantee that it's a new phone as Apple sends it from overseas in a brown box and they only know that the front, back and battery is new. I don't want someone else's old second hand inside. I want a complete new phone if they are replacing it.