If you have not spent that amount you need to contact your credit card provider asap and put a stop on it. Check your purchase history in case someone has used your account. If so contact the seller to cancel, and then ebay using using callback on here:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
And change your password. In your My eBay > Account tab (near top left) > Personal Information > Sign in and security > Password > Edit