Other telco also do the same, offer only for new users. Legacy plan stay forever expensive until ppl want to port out baru nak offer. Hence once in a while, do a review of your mobile plan and take action. If you can, check what plan your parents are using, update them when necessary so that they don't continue paying for something which is not relevan.
What MCMC should do now is to try and improve indoor coverage as much as possible.