can anyone help me

i use this phone for nearly 1.5 month.. im using digi family postpaid, not on smart plan.

i checked my bill, they charged me rm90 for gprs which i never use at all.. i already disable the mobile network. i only use wifi for internet connection as most of the places i've been got wifi, furthermore im not using internet that frequent

i asked digi centre, the guy said eventhough i disable the mobile network, the phone will continue transferring some data from time to time as long as it has sim card in it.. meaning that it keeps on using the internet connection for update or sync (eventhough i manually off it).. he said it is one of the feature of smartphone that most consumers dont know about it

the only way to stop from overcharged gprs in my bill, is to:
1)subscribe smart plan (unlimited access), or
2)disable gprs (meaning i cant browse internet unless on wifi only, cant send or receive mms),or
3)change to non-smart phone

anyone having similar situation with me? or is that guy just bullshitting me?

alr did that since day 1.. still being charged