Rain and taking peoples money without explanation

Help me understand because clearly they couldn’t. I cancelled my subscription before the day of deduction which is on the 15nth of every month, I understood when they took the money on that set date because maybe it was already on running. Tell me why do they have to deduct again on the following month without me even used their data since the month of cancellation, they’re busy telling me that it’s an outstanding amount! For which month exactly because I’ve paid my dues. I sent an enquired which was attended to, the support team called me and failed to answer my queries then hang up on me😂