Telstra mobile extra data clearance

Product Name: Telstra mobile extra data clearance
Is this even legal? Telstra automatically upgrading me to a more expensive plan without asking. Currently paying $39 month-to-month ($10 monthly discount at signup) for 15gb. : r/AusFinance clearance, Telstra launches plans without excess data (with a catch) – Pickr clearance, EXCLUSIVE: Telstra's new look mobile plans: Unlimited is back! *AT A PRICE » EFTM clearance, Is this even legal? Telstra automatically upgrading me to a more expensive plan without asking. Currently paying $39 month-to-month ($10 monthly discount at signup) for 15gb. : r/AusFinance clearance, Telstra prepaid plans and recharges compared | Reviews.org clearance.