Vodacom Data *******

My data has just vanished all 28gigs, i was given back 5gigs from vodacom as a gesture of goodwill. I have a data contract since November 2018, i have never ran out of data to date, i have app monitoring tools and the vodacom app to monitor usage but they still say the data was used. They cant say on what or where but all of a sudden half way through the month 30gig data gone and all they can say is they dont know what happened because they dont monitor sites or devices!!! This is the pathetic level of service from vodacom as i am paying for that service every month. Data cannot just vanish especially 28gigs and then vodacom gives you a gesture of goodwill with 5gigs back after taking 7 days to investigate whereas i had to buy data in the meantime!!!