Billing deceased people despite timeous management by surviving family

My father passed away last year. He had two unexpired phone contracts and three month-to-month/expired data packages. I visited the local Telkom branch with all the relevant documentation and requested that his phone accounts be transferred to my name and that the data packages be stopped. I was assured that all of this had been done. More than a year later I am informed (by a debt-collection SMS to his old number) that Telkom never stopped the data packages, and they consider my deceased father to be in arrears with his account - by thousands of rands. What *********** nonsense is this? Obviously my documented proof of his demise, etc were considered adequate to rtansfer the phone accounts to my name, but they couldn't be bothered to change the rest because they were cancellations not transfers?