WHERE IS ALL MY DATA GOING AND SHARED DATA RECEIVED IS NOT WORKING!?!?!

I keep buying data but it's always finished, and NO I'm not using it, I have wifi at home and at work, hardly use it outside these places. My shared data from a family membet isn't working either, keeps asking me to login to buy data, but there is 2GB available?!?!?! Called MTN and was cut off, lady told me to restrict my background apps. Biggest nonsense I have ever heard, I was with Cell C for years and years, 2.5GB lasted me longer than 30 days and stil had 1.2GB left every month, and NO I did not change any settings in my phone, so why is it now that I never have data!?! Since moving over to MTN and after downloading the app all this started. After every call I get stupid automated messages from MTN, have disabled everything but it still comes through! I dont want any messages from MTN and I want my data refunded, never had so many issues since moving over to MTN!