Vodacom Fibre *******

I cancelled my month to month fibre service a on the 3rd of April because I was told that I need month long notice for cancelation. The services are due to be shut down on the 1st of May. However, my bank account got debited on the 26th of April. Do we not pay in advance for services? Meaning that the debit order end April covers the month of May. I feel ****** because my services end May 1st but already already paid for the whole month of May.