Bills still arriving for my deceased mother's landline.

My mother passed away in early October 2021. On 15 October I notified the relevant authority at TELKOM - (LSDA National) and requested that they disconnect my mother's landline and terminate the account. I submitted the required death certificate. I received a reference number. Subsequently, someone has accessed the phone in the care home. We have been billed increasing amounts - R353 in November, R444.02 in December and now R500.00 in January. This individual was 'discovered' and has subsequently been disciplined and lost his job. We have sent subsequent emails, but still no response and the line remains open, with us liable for monthly rental. I cannot stop the money from being drawn from my account because I trusted TELKOM and signed a debit order. This abuse of the phone is not TELKOM's fault directly, but if they had disconnected the line as requested at the end of October - or November at the latest - we would not have gone through this whole harrowing experience. When will my deceased mother's landline eventually be disconnected? Who knows.