dissapearing airtime

I switched off my data connection and put in R12 airtime. I ddnt get a confirmation sms so I checked my balance and it was R12.01 then I immediately switched off my phone. when I switched on my phone and tried to buy data there was no only 0.01 left. when I call vodacom customer care they told me that my data connection used up my airtime. BUT MY DATA CONNECTION WAS OFF!! ! !!!!!. this is just unacceptable.