Suspicious airtime theft

I recharged with R35.00 Cellc airtime on Monday the(5 November),an amount of R4.00 owing was deducted from the amount,leaving me with a balance of R31.00. To my surprise on Tuesday as I tried to make a call I was told of insufficient finds. Unfortunately this is not the first and I have been monitoring this trend,thinking it could possibly be due to app updates,but it is not the case.This is plain ******* and would like this injustice to be dealt with.