score:7
Own experience/common knowledge answer, so no links.
If you booked a ticket on which there is no free cancelation within the last 24 hours, you owe the company the money. If you make it impossible to get the money from your debit card, you may be charged in an other way.
Your best bet is to claim back from your travel insurance.
Sometimes companies allow you to change your booking to a date in the future rather than canceling, you will not get back (or not pay) your money but you might be able to get the date changed to a date you can travel.