My dad has a contract with them

My dad has a contract with them. He passed away last month. I contacted them via email and telephone to inform them of this and to cancel the contract. I also wanted to settle any outstanding amounts and convert the number to prepaid. I received a reference number via email a few days after I sent it and thereafter nothing. I phoned the customer service and still no joy. Their agents take forever to answer the phone and when they do eventually, they don't know what to do or even route me to the correct department