i recently got an iphone and i tried to activate it but when i called they told me it was activated under a number already. i called the person i bought it off of and they told me they switched to at&t and they also switched numbers too. they're using the number on at&t that the iphone originally had. when i restart it it says the phone is not activated yet and to activate it, but when i do it's "already activated under another number". is there any way to fix this without the person i bought it off of?