Given a Heroku employee showed up in a different subthread of this comment section saying thay wanted to change things but couldn't, in spite of a long discussion between the technical and legal sides trying to find a way to do so, it seems to me to be at least plausible that in this case for whatever reason that wasn't an option.
If you want to do a close read of the terms and conditions/contract language as of a reasonable guess as to when OP signed up and link the section you believe does give them the right to make such a change unilaterally, I'd be happy to read it and discuss further.
My current position in the mean time will, however, remain that while there's always a chance (often a pretty good one) that my hypothesis is wrong, claiming it makes no sense at all is a stronger claim than is justified by the information forming the basis of this discussion.
If you want to do a close read of the terms and conditions/contract language as of a reasonable guess as to when OP signed up and link the section you believe does give them the right to make such a change unilaterally, I'd be happy to read it and discuss further.
My current position in the mean time will, however, remain that while there's always a chance (often a pretty good one) that my hypothesis is wrong, claiming it makes no sense at all is a stronger claim than is justified by the information forming the basis of this discussion.