Charged for calls not made

On my July account it is indicated that I made 28 local calls, 6 long distance calls and 2 mobile calls. It however does not indicate during which period these calls were made and to which numbers. I very very often make a long distance call, maybe once in two to three months and I never phone mobile numbers from my Telkom line. The 28 local calls also seem extravagant to me. I logged the same query on the Telkom website but nobody contacted me to resolve it.