Missing Airtime

I am currently on Power Bonus price plan, each time I recharge I receives extra airtime allocated, however on Wednesday 02/02 and Friday 04/02 after I recharged when I make phone calls the network deducts such airtime from my real value airtime instead of extra airtime allocated, which(extra airtime)'returns to Vodacom, thus far I have lost R1.85(Wednesday) and R0.13(Friday) all together it amounts to R1.98. Well, one can say the amount I lost from my real value airtime is nothing, but it must be returned Furthermore,I need Vodacom to investigate and rectify the problem ASAP.