R2327.73 BILLING FOR DATA INSANE

i have logged a complaint last week and still no solution , my tablet was open line when i took it out on contract i was not informed that it is a open line or asked if i wanted a top up or open line the tablet comes with 500mb every month and i make sure that only that 500mb gets used. i had to wait 3 month to migrate my contract for the first 2 months i paid the standard price for the contract come month 3 i finally get to migrate then a get a bill from vodacom stating i owe them R2327.73 only for data i cant see how that is possible i make sure the data is switched off unless im using it. i just dont think its fair for me to pay so much only for data ive been a loyal customer to vodacom for 4 years and i never had that problem and now i have a huge problem. if i dont pay that money i get blacklisted if i pay it off my 3 contract lines gets cut so can u please tell me what the solution is here because i cannot handle this stress anymore