Telkom complaint

My dad has a Telkom contract and they over bill him with R500 for an apparent over usage of data, but he has a capped contract. He called their contact centre they apparently cannot help him and he went to their store they showed him away saying he should call the contact centre. He's unemployed and don't have the money to pay for things he didn't sign up for. They don't want to assist him and refuse to even listen to him