MTN *****ing my data

I am a prepaid customer that recently ported my number from Vodacom to MTN, a week ago and starting to regret it already! On Vodacom, the month would run out before my data did, every month, and I battled to use all my data up before I ported my number. I had 1.5 gb data a week ago, and now I have less than 500 mb. At work I am on wifi all day. At home I am on wifi permanently, so where is my data going MTN??? The only time I am off wifi is while I am driving and I am definitely not browsing the web, or downloading anything while I am driving. Please explain MTN, or in 3 months time when I can port my number again, I will be gone!