Where was it bought? Do you have evidence of buying it on credit card? You don't need to have registered it for the warranty to apply. The store where it was bought will probably have evidence of it being sold, for example. I'd go back to them in the first place, anyway, to describe the problem. Stores aren't in the habit of accusing of past and potential customers of being lying about something that has broken down, and you have rights such that it is worth their while treating you as saying the truth and maybe losing the cost of a charger rather than being taken to court.

Edit I don't know how the rights thing applies in an international situation, though.