Data billing incorrect and too high

On 2 February 2015 I received an sms alert from Vodacom stating that my data usage is too high. I phoned Vodacom customer service and log a complain and they said someone will phone me. I took the phone to Vodacom Technical shop in Somerset wes and the technician said there is something wrong with phone. The phone is a Samsung S5, all data switched off but phone keeps downloading. Phone was booked in and mother board was replaced. I have phoned Vodacom customer complains another 8 times and went to Vodacom shop to follow up on complain. Today 18 days later Vodacom still has not respond. Vodacom claims I have a data bill of R5951.96 and I have 1 Gig data on my plan. 5.090,200,640 data usage on 30 Jan which is impossible. Vodacom is very eager to sell us phone and data contracts and to debit our bank accounts, wish they were this eager to sort out our customer complains and queries