Downloaded music by accident do no want to pay for it

The official position is that all purchases are final (since you can't very well return them). The Store has been known to give a refund as a concession where, for example, a small child has made the purchase without permision. I can't say whether they are likely to do so in your case; you can only ask, but please be aware that they are under no obligation to refund you. Contact them at https://www.apple.com/emea/support/itunes/contact.html