You can contact eBay's customer service by calling 866-540-3229 or on the website. The most common reasons to contact them are when you have an issue with a transaction that was made on their site, when you're having difficulties using PayPal or using your bank account as a means of payment, or if you are suddenly facing a few issues with the site itself. If this happens, make sure that you log into your account and see if there is any suspicious activity in it and then call them for support.