No assistance in cancelling contract for a deceased

My fater passed away and we went to MTN to cancel his contracts. After about 2 months it is still not done. Every time I phoned them the agents said they needed to speak to the account holder, even after I said he is deceased. Now they say there is money outstanding before they can cancel the contracts. If they cancelled the contracts on 4 June 2025 there would not be an outstanding balance. This is unacceptable!