I do not know what to do; the service was shocking!

My husband (I am *** by the way) had a phone contract with MTN that expired in June that he did not renew but continued on a month to month basis as he was very I'll. He passed away end July. Mid August I went into their local office and gave notice together with all the necessary documents that were submitted for cancellation upon death. The death certificate and all necessary documents were scanned and sent to their HQ. When I inquired 2 weeks ago I was shocked to be told that his contract had been renewed for a further 2 years. They could not verify who/when/how this was even possible as he was in palliative care since beginning of 2023. His account was dt till the executor had his bank accounts blocked. All the correspondence was again sent to their legal dept. Received a message on his phone that is not used, that no calls can be made, due to an unpaid amount. The most shocking service I've encountered under the circumstances. What is my next step?