BONITAS I need answers.

I was a member of Bonitas medical fund for over a year, due to change of employment I had to cancel my medical aid. I recieved my cancellation certificate in August 2018 as it was my last month with the medical fund and in September 2018 I joined a new medical aid scheme. SOMEONE PLEASE TELL ME how is it possible that I get monthly statements from BONITAS from September 2018 up until January 2019 yet I was nolonger part of their medical scheme, how is it possible when I was nolonger their client? Month end of February 2019 I get a statement stating that I owe them, but how do I owe when I had savings before my cancellation and if that is the case why did I receive the statement 6 months after my cancellation?