If it is a transfer through your bank account then you use the bank account number.  

It is only when you pay through paypal that you have to option to use either bank account number or debit card number

The OP said they paid by bank deposit (not Paypal). So, unfortunately it would not be considered a visa or m/c debit card transaction and not be eligible for a chargeback. That is what I was trying to establish.

Also if a person buys an item at a shop via eftpos using their visa or m/c debit card, they would need to choose 'credit' rather than savings/chq to be able to request a chargeback later on, for legitimate reasons.

Handy tip about the mastercard debit card.