You must have made an offer, which was accepted.
Making an offer is a commitment to buy if the seller accepts it. It doesn't need to be confirmed.
Because so many buyers were changing their mind and not paying, eBay now enables sellers to require instant payment when an offer is accepted. You must have provided a payment method when making the offer, otherwise eBay could not have taken it from your account.
All you can do is ask the seller whether they are willing to cancel the sale, and refund you, but they don't have to. Alternatively, they may agree to a return request - but again they don't have to, unless their returns policy is to accept returns, which will be stated in the listing. (UK business sellers are required by law to accept returns for online sales, but private sellers and sellers in other countries are not.)