1.5 GB data just taken

I had 1.5GB data on my cellphone yesterday (25-08-2015) morning at 4:00 am, I went online with my ABSA banking app and loaded airtime for my daughter at about 04:12 am, when I checked my data again i had a null balance data. Your Call Center agent wants to advise me that the 14 seconds that i used the banking app the 1.5 GB was used as if I am an idiot because there is no device that downloads 1.5GB in 14 Seconds. This morning I phoned your call center again and Busi told me that no query were logged and that she cannot log a query because my invoice has not been closed off for the month, thus the contract customers does not get any priority at all. You receive your payments every month without delay, my account has never been in arrears and this is the kind of customer service I receive, i must wait until your staff decides whether they want to investigate my query. I have taken screen grabs of my cellphones data usage as from the 15th of Aug - the 25th of Aug and my phone only used 424MB and up to the 26th of Aug 459MB. I will not leave the matter alone as I want my DATA back that you took!!