Still debiting credit card after service has been cancelled (and confirmed)

In the past, I experienced a very decent speed with my 19 hour uncapped SIM card. 10Mbps upload was the norm. The upload speed dropped to below 500 kbps maximum in recent times. Any time of the 19 hours.

I cancelled in May and received confirmation that the service stops the end of May. But at the beginning of June, they still debited my credit card. (Un)lucky I stopped using the credit card and the card was declined, adding a penalty amount as well.