Buyer not paid - how long to leave it and what now?

[unlucky83]

I am more or less an ebay seller novice...
This is a cheap item (80p plus £1.17 postage). Listing finished on Christmas Eve. Buyer still hasn't paid - have sent 'send payment details' twice.
No idea what I am supposed to do now - actually now I'd rather they didn't buy it ...it was a present, a duplicate book and DD2 has just ruined the copy she has ...
Do I email them and ask if they want to cancel? Or?

open an unpaid case - wait 4 days and close it.

how long do you have to leave it before you do?
Is 7 days long enough? Especially at this time of year?
(buyer has 100% feedback - would a case negatively effect that?)

you can open an unpaid case after 48 hours. Yes of course they have had enough time. Time of year doesn't make any difference.

A buyers feedback will not tell you how many unpaid cases they have had no.

Thanks Ill do that now ...