recharged and airtime vanished

On Wednesday 17 June 2015, I recharged my Vodacom phone with R55 airtime (balance after recharge being R86). I didn't use my phone to make calls or send sms's, I have a blackberry and my BIS expires on 23 June, yet yesterday (18 June when I wanted to make a call, I had R1 airtime left? I checked all dialed nrs on my phone, nothing was made during that 2 day period. What the hell? I didn't subscribe to anything and I don't understand where my airtime has gone! This is totally unexceptable! I only use my phone to keep in touch with my parents who live in Mpumalanga.