i am on a prepaid plan, $2 charge per day if used. But on some days, although I have the mobile data turned off and not making any calls, Optus still eat up the money.
is there anyone else having the same problem?
I'd keep a record of any whole days you have the phone off in this way. At the end of the month see if you and Optus agree and if not ring up and request a refund.
Also try airplane mode perhaps instead of mobile data off. It only takes 1 byte to trigger the $2
I do think OPtus should provide a tiny buffer of allowance on a plan like this. Perhaps 100kb just to catch issues like this.