Telkom inconsistent billing

I am a regular user of telkom lit video service. As of this month they have doubled the prices of their video bundles which is extremely disappointing. I loaded a bundle a few days ago, according to my data logger I used 1 gig of data but when I check my balance it shows that I have used 4 gigs, I know data loggers are not 100% accurate but a 3 gig variation is not possible.