vodacom data dissappearing

my Dad bought 3gb data on the 22th of May on his wifi and we went on his internet banking and was about 10 min on the internet and when he was done i wanted to go onto the internet and when the browser opened and told me that the data bundle has been depleted!!!!

How does this happen?

it happened to me aswel a few days ago bought 2 gb on my phone and the day after i bought it i only had 100mb left.

really vodacom - if you do not fix this we will cancel our contracts and go to someone else.

how will you fix this problem as we will not buy more data due to this problem

i want this sorted as soon as possible please.

i liked vodacom due to not having problems but since this data just dissappearing without being on the internet and no apps running to use the data, im really dissappointing.