MTN debiting for deceased husband’s cellphone 5.5 yrs later

I cancelled my deceased husband’s cellphone in 09.2016 and have written confirmation from MTN that it was cancelled. At the end of November R2300 went off my account for his phone. I stopped the payment, went to see MTN and gave them copies of the original documents. Despite following the matter up during December a double amount of R4600 went off my account. Nobody in the Cresta branch is concerned and are blaming the legal department. The legal department is blaming the store for not getting ANOTHER current letter telling MTN to cancel my deceased husband’s account. I am absolutely furious and don’t know what to do.