If the user has changed phones (even keeping the same number) or has for instance begun using 5G (which wasn't available 5 years ago...tmo started rolling it out at the tail end of 2019), they're using a materially different product than they were originally contracted for, and have likely agreed to new terms. Not saying that isn't scammy or scummy, but just like you've changed the product you're using, they can change the product they're selling.
In Washington state electric vehicle owners pay a large surcharge on our annual car registration fees, meant to replace the gas taxes we're not generating.