Very bad service/Very expensive network

I bought a Vodacom R55 and a vodacom R40 airtime.That means in total you get a R95 bonus airtime.I checked my airtime balance it was there.I went on the internet for about 20sec,when I locked out,I checked my balance the bonus airtime was gone.I called Vodacom to asked where did my airtime go,the lady told me you used it on serving the internet.Now you tell me is that possible to use R95 airtime for just about 20sec!I can't believe this,Vodacom is a very expensive network.