Dissappearing Airtime

<p>I'm a vodacom network user.i had plus 20mb data & R50 airtime.i browsed the Internet & downloaded 40kb,48kb & 241kb pdf documents in less than 5 min.by the time I received an sms prompting that I have 4.5mb remaining I immediately switched off my mobile data. I tried to buy more data but to my surprise I was left with R2 plus a couple of cents & still had 4mb remaining.i contacted customer care & spoke to Lerato ***aze,explained my story & she told me she cannot help nor escalate my complaint that " why was I not prompted that my data is depleted before being charged from my airtime or get an sms that my data is not sufficient & will be charged from airtime?"</p>