Disappering Data

4 mnths ago experience high cellphone bill that I couldn't explain and when I phone the network was told that its was my internet usage etc. I even asked them about pay as you go options because found myself having to top up data that was disappearing and couldn't understand how so. I then started monitoring my usage and the past 3 months the bill drastically decreased MIND you not that hv limited my usage. The only I 've bn doing is monitoring the balance almost every day. Then last week on Sat, 15 Aug had about 800 MB but on Sun woke up to NO data. I was livid, I couldn't understand it. Later the same Sun bought 500MB and monitored them as usual n Sat had about 400MB but woke to depleted data. I did not buy a smart phone to have limited usage on it jst cause my cellphone will rob me/ milk me out of data. THIS is so infuriating in so many levels.