DATA ******* WITH NO PROPER EXPLANATION!!!!

From the 15th to today I have noticed my data is finishing faster than it should. So in 9 days I have used 20g, then in one day I have used 2g+3.5g+6g, this is so wrong what MTN is doing to us. In normal circumstances my data lasts me for a month. First they over charge us and now they are literally *****ing our hard earned money. I called MTN and they said put ur data off, go to each app and change the background settings. I did all this and guess what at 00.46 last night my phone data was off yet this morning I get up to a message that my data is at an 80% usage level, HOW MTN, PLEASE EXPLAIN HOW????