My friend’s message randomly started sending from a new broken number

For no reason my friend who has a Samsung’s replies to my texts have started sending from a broken down version of her number. When I try to reply to that number I am met with an error invalid number message, but when I reply to the conversation we have been using for months, her replies come in from the broken number. I tried blocking the broken number but that only blocked her along with deleting the broken number, but it reappeared when she replied. What can I do to fix this? I really don’t want to delete our message history.