Harassment and incorrect billing.

I was contacted last week by Cell-C stating that my account has been handed over for collection. My account billing date is the last day of the month. So how is that I am handed over for account collections. Secondly, The amount I am being handed over for does not match my Billing Invoice for the 30/04/2023.The amount I was harassed for was R190.00 but my online billing says R80.25. Cell C are a bunch of children and neither one of them knows whats going on with their systems.