I upgraded my existing iPhone 11 to a new iPhone 16 Pro. I went through the Quick Start process, which took several tries (turning off phones and restarting the transfer). Everything seemed to go fine - the new phone makes and receives calls and texts, my photos and texts transferred, my apps transferred and work, etc.
The issue is that my old phone still works. When someone calls, it comes in on both phones. The same with texts - I get the text on both the old and new phone.
I need to return the old phone for a trade-in, which involves erasing data, etc. I'm concerned that