Complaint about a cellphone and a sim card

Good day, my father's contract on mtn expired on August 2016. And he negotiated with mtn that he is not interested in a new phone but an airtime was fine. He was given an airtime of R384.99 monthly, this year they called him before August and they told him that on August the airtime is going to be expired. And he said to them he doesnt want anything from them again even the airtime because he is no longer working he wont be able to pay. And they said they will be able to diactivate the contract at the end of August.. and they didnt call him so my father passed away on 10th of September, and we called MTN Legal department on the 03 of November and they said we should send the death certificate, copy of id and proof of payment and we sent them using Email. After they received the Email they blocked the sim card and the cellphone whilst they agreed we will use the phone as prepaid not as a contract phone. And we need to use the phone to diactivate the other accounts of my dad now we cant cause mtn blocked the phone. And they are not willing to hear anything from us but they blocked the phone because the owner passed away.