lost airtime

I upgraded my phone at a local vodashop and recievedvmy new phone and sim. woke up with a shok and when i checked my top up balance this morning it was 0! phoned customer care and I was send from one department to another but no one can assit! if i was told i will loose my remaining R200 airtime i would have waited thil the end of the month. i paid end of may for this airtime, how can they just take it away? its *******? this cant be legal? please can you assist? ***