Outrageous amounts on Cellphone bill

I need help with Autopage please. they charge you outrageous amounts for data charges. for example R2300 for 1300 MB of data. they cannot explain to me why. i tried explaining to them that i have WIFI and my cellphone data isn`t even switched on but they don't want to listened. please help me with this. i have been too the Thabazimbi and Witbank branch and they say we must just go to head office which is in Johannesburg. when i phoned head office they said they will come back to me but they never do. this has been a week ago. this contract is on my parents name and they are pensioners. i personally assisted them with the WIFI and they cellular data to switch it of. i am not receiving any viable answers from them. their attitude is clearly we know nothing. their service absolutely stinks. i really need help guys as my parents cannot pay this amount and i feel that they will sue them for the money and this will lead to a bad credit rating and Autopage knows this and they will milk them for every penny they got. this feels a lot like ******ion and ************