Debit card transactions are routed based on BIN which is usually the first six digits of a card number. If a merchant either miskeyed an account number or intentionally forced a transaction through on an invalid card number that has your BIN, then the transaction will be routed to you.
If the merchant failed to obtain a valid authorization as required by VISA/MC rules, then you should have chargeback rights to send the transaction back to the merchant. Exceptions to this would be if the communication network was down at the time of the transaction and the merchant used a "stand in" authorization or the dollar amount is below the minimum chargeback threshold.