secure checkout leaks like a sieve

having purchased an item via ebay i was referred to the company's market place interface to pay for it. however due to loss of replacement card (old one expired) i had to wait for a new one with different numbers on it. mysteriously, i received an email confirming checkout was complete for something i hadn't paid for. note that the email has no shipping added, no billing or delivery address and no card number. the emails, thankfully, are saved on google's server. i switched to gmail after strong suspicions that i wasn't getting all my emails via my own isp.