Telkom number hacked

My Mum's landline number was hacked and that person made calls for more than R 2000. Telkom was the one's who investigated and told my Mum her number was hacked. Now telkom insists that my Mum pay that amount. My Mum is a pensioner and won't be able to pay off that amount. And now Telkom is harrassing my Mum. This is unacceptable. My Mum's landline number is ***. Please sort out this out ASAP