Data Gone missing second time

On thursday 3rd December 2015 i recharged with R99 data for the 500MB, using my laptop i connected to the internet for a few minutes, then on Friday morning i tried to connect again only to receive a message that i have run out of data. This is the second time it has happened and when you call the call centre they don't even seem to know how to explain or they don't have a clue of what they are doing. Is there a way to check this because am really getting frustrated. The lady i spoke to on Friday said that maybe its the applications on the phone but its not on the phone but for my ****le when the laptop is off i don't expect to lose data. Can someone explain why am losing data