I'm currently on a Telstra BYO plan for $39/month that gives me 30G of data each month. They've sent me an email today that they will upgrade me to $45/month for 40G of data. (It will increase to $55/month after 12 months). I never get close to using the 30 gigs every month, so the upgrade is unnecessary.
I looked through their site and FAQs and it said if you don't want it you can cancel your plan or join a different one (all more expensive).
I'd like to stay on this one. Has anyone been able to stay on their old plan at all? Is there any mechanism or advice to do this? Their call centre is basically operating on thin staff levels "due to Covid-19" and sending a message through their Telstra app meets their Codi Help bot, which isn't much help.