Billing continued after cancellation not processed

My 80 year old mother gave a months notice on her landline on 30 Jan 2018 when she was moving. It took a couple of the months for the cancellation to be processed and Telkom continued billing her. Due to this outstanding amount she couldn't get a phone installed at her new residence, despite having been a loyal customer for 40 years. She has now been handed over to a collecting agent despite continuously attempting via a Telkom branch to get this corrected. This is impossible and such a shame that this is how loyal customers get treated, it shouldn't be so difficult to interact with Telkom. Please can we get this resolved and the arrears written off.