Telkom useless

My Mum's landline number was hacked. Telkom investigated and confirmed to her that airtime was transferred from her landline number to cell number ***. My Mum does not know this person. Telkom open a case and then after few days said my mum must pay the outstanding amount although it isn't her fault.The amount was over R 1600 now Telkom adds interest every month.My mum is 67 how on earth would she know how to hack a landline. Telkom is harassing her for the money. My Mum is a pensioner , where will she get that amount to pay Telkom. I've queried this on behalf of my Mum and sent all the required documentation. It's been over 2 months with no reply.