I just got this iPhone and had my number transferred to a new carrier. But my old sim is still in my old phone, and when people reply to my messages, they exclusively go to my old phone(not my new iPhone).
iPhone 11 Pro Max, iOS 17
It sounds is if you perhaps did not properly prepare your old phone to be given to someone else. This is not good as it means that the phone may still be connected to your Apple ID.
See here:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
See the section for what to do if you no longer have the old phone.
Probably it’s temporary you should contact your carrier and ask. But if the old iphone is in the same Apple ID account, you can go to Settings>Messages>Text Message Forwarding> and toggle your new iPhone
Messages are going to old phone
