bad explanation

Why is that when I joined this company no one explained to me that I will be insured from the 1st till month end.even though my account is debited on the 15th of every month? Only when I CANCEL then Im told that I will no longer be covered as a result I owe the company for insuring me for 2 days, I cancelled this policy on the 2nd not month end because I wanted them to debit my account and to my surprise I owe them for 2 days. Does this now mean I didn't understand when I joined or it means I never read the fine print. However all the insurances are suppose to cover one for a month and this one covers me for 15 days. It means they owe me for the past month. Can I get a clear explanation as to how it works so as to help others before they find themselves without an insurance like me.