"Over charge on care"

My parent is in an Opal care facility. They have been there for nearly 12 months. At approx mid year they received a charge for accommodation costs.

I rang and spoke to aged care and they confirmed my parent was fully supported.

At the time of writing this, I have someone from Opal calling and emailing saying my parent, who is 95, owes over $8000. I have spoken numerous times to Aged Care/Centrelink and they have all confirmed that my parent is fully covered. However the person from Opal doesn't understand this, I have given them reference numbers and names, have advised them that a letter is coming but due to a system change it is being delayed. This person keeps saying I don't understand and charges keep occurring!