Woolworths service disappoints

I have been trying to get Woolworths to close my late mother's account for almost 2 years. I have sent them copies of her death certificate and her ID on several occasions but to no avail. But every month Woolworths sends me an SMS to remind me of how much credit my mom has on her account. I have been in touch with so many departments but no one responds. What is a person supposed to do?