Cancellation Issue - Deceased person

I have been trying to cancel a contract with Vodacom since the 12th of December 2019 for a deceased person - I was told which supporting documentation to attached and provide, which I did. I have been receiving the "Successful Delivery" and "Read" receipts from both email address used to send the documents to "***"and ***. The account has been unpaid due to the deceased bank account closure and I still receive monthly invoices and statements. I keep trying to call but get transferred from pillar to post with no luck. I even tried going back into the store - but they cant help either. What is an acceptable time frame to wait for Vodacom to complete this seeing that you can open a new account and walk out the store within an hour. Poor and shocking service - I hope that Vodacom employee's family members don't have to deal with this same situation.