Being billed in insurance on closed account

In May I payed up and closed my Mr price account. I made a trip to the Pavillion store where I was told by management to fill out an Account closure form which I did. Today I received a statement whereby I am being charged for the insurance benefits and now I have an instalment due on an account I closed 2 months ago. Clearly the paperwork was not submitted I will not be paying these fees as I have closed the account! This needs to be resolved