Transfer

My Aunt passed away in 2020 and i was given her phone, i never figured out how to pay her phone bill so i’ve been using her icloud to text ppl using wi-fi . it is now 2024 and i have a lot of messages on the icloud and the phone is damaged with a green line going down the middle. at&t has sim locked the phone bc the phone bill was never paid since she died and gave the number to someone else, i didn’t know her at&t login to pay the phone bill or even how to receive a new number with it being sim locked, i want to know can i buy another iphone and transfer the icloud from this phone to the new one (the old messages and pictures on the icloud ) while adding a new number/sim of at&t to it while keeping my contacts and the messages associated to the other device ? also, the contacts i’ve texted with icloud will they get a new contact from me (the number) or will i be just texting them off that same icloud from before just with the number added ?