DATA missing

i have bought 500mb on the morning of th 29th of March at 6:38. i updated my whatsapp, switched my wifi device off at around 6:42. Between 16:30 i used the device on and off to use my what'sapp till after 9pm. the morning of the 30th of March i was notified that i have less than 4mb left.....phoning the call centre and it's just, oh sorry, we don't know what you used your data on. Well let me tell you, NEVER EVER have i used 500mb in 5hours by just using whatsapp!!! so i basically just have to accept that i have lost the data