No affordibilty checks done by Vodacom

I got a 2 for 1 contract when I upgraded my phone and gave the one phone to my 9 year old son to use. He received R66 airtime per month according to the contract but at the end of April I received a R1079 bill from Vodacom. I contacted Customer Care and they informed me that he subscribed to a new contract on his phone number and that there is no way they can cancel the contract but not refund me. My concern is that I can't afford that contract and that none of my information was verified or an affordibility check done before they upgraded my existing contract. There was no security check done to see if I authorized the upgrade and none of my personal information was checked. I am highly dissatisfied with what happened.