Cellular Data

I have a contract with Cell C which is supposed to provide 200MB of data per month. During the month the service is very very slow, sometimes can't even use it, very unreliable. My data is generally switched off, I use it from time to time however definitely not to the point of reaching the limit. For months now, I have had poor service and intend moving to Vodacom as contact with Cell C regarding this problem has had no succes. I would mention that I pay R703 per month, I utilize data mostly from wi-if networks as I'm generally in a wifi zone. This is an iPhone 5s and most of the apps that use cellular data are turned off for cellular data use therefore how is it possible for me to reach the 200MB limit? I am a long standing customer.