loss of excessive data amounts

Telkom has been contacted on numerous occasions to assist us with or advise where or how 10gigs of data can disappear in the space of a week. There is no downloading, or multiple devices uses this account, no excessive use or all day use on this account. We are not being assisted in any way regarding the above. So basically what and who are we paying for? Kindly assist or advise in the steps to be taken.