hiya,
i work for a leading credit card firm in england and have worked in the Chargeback dept for many years now.
when a customer disputes a transaction the first thing to do is get a dispute form out to the customer, when that arrives back it gives the bank the authority to request a copy of the sales voucher(visa regs state the merchant has up to 60 days to provide), when this is received if it turns out to be fraud i.e someone elses details then the bank have the right to return the charge back to that merchants bank and credit the a/c accordingly.
it would be then that the bank block the card and issue replacement with new details. however, if a customer disputes numerous transactions or its an already known fraudulent merchant then the card is blocked immediately. i really think this is down to the individual organisation.
if the transaction is from a counterfeit card then the bank used to take the loss but with chip & pin its different. the liability is on the merchants side, if a card is a "chip & pin" and the merchant accepts it as a signature then if it turns out to be fraud the merchant looses. but the customer will not stand the loss unless they have given their pin number to a 3rd party or allowed access to it by writing it down(even when disguised as a phone no etc)
now i hope this clarifies things a bit.
sinead
xx