Can not cancel my deceased father contract

My father passed away 2.5 years ago. My poor mother has been to MTN countless times to cancel his contract with the death certificates and other documents but MTN is still making her pay for this account. MTN simply cut off her mobile service until she pays my deceased fathers bill.

Now to add further insult, it appears that whilst trying to cancel this contract MTN ******* her into upgrading the wrong account and she now has an extended period period on this inactive contract.

This is blatantly unfair and bullying practice. Is there anything that can be done ?