Data and airtime depleted

This morning i had over 150mb of data and i had airtime. All i have been doing the whole day is surfing the net on my cellphone... no videos and no downloads. I made two calls during the day and when i checked my airtime balance it was on r8 after the calls. Funnily enough a few hours later after making the calls my airtime got depleted even before my data was depleted. There is definitely some sort of foul play. Im really not impressed. Im actually looking to switch to a competitor because i have seen from past experiences that they do not inflate data charges and ***** airtime from consumers