Digusted, upset, sick and tried - literally

Vodacom made a mistake and now I have to pay for it. Took out a top up data contract for my son in December 2014, got a shock bill 2 months ago and called to enquire, still unresolved? Second shock bill last month R7410.93, apparently they put my sons contract on an open plan instead of top up and now want me to pay? The vodashop that facilitated the deal don't want to accept responsibility and Vodacom are not listening to my actual issue...? Regardless of what the bill is, I never asked for an open contract, if they had put me on the contract I asked for in the first place, we wouldn't be in this predicament? They keep telling me that they willing to reduce the bill, but I know I am not liable! Give customers what they asked for and stop trying to bully us into submission when you have messed up? The worst experience of my life, still unresolved...? I am physically sick. Even after taking a day off work to go to vodaworld in Midrand, and making numerous calls to their useless call centre. Why would I have a top up contract for myself and then take out an \open plan"contract for my son"