Constant data depleted

I have two contracts, one for phone the other one for data. The data contract , for two months, starting from November and December 20 Gigs of Anytime data that usually lasts me the whole month, for the months mentioned it has only lasted 10days, then it's depleted without fail. I have had to spend close to R300 in data top ups for data on the cellphone contract since it finished on the 7 December. My monthly data top under the data contract agreement is loaded every month on the 27th . It's ridiculous, I don't know what is going on. My data utilization has not changed much from all the different months prior to November, for whole 20Gigs of data to be depleted in such a short period of time. I didn't go to YouTube any differently from the way I would during the month of October going down.

I need explanation this , I am spending a lot as it is on the two contract payments, to have to Top Now each month😖.