Unauthorised payment help

Opera14

Hi, I just sold something on eBay for around £350.

The buyer has 0 feedback (even though I stated to contact me if you've got less than 10 feedback before bidding!).

I received payment for the item today, however, straight after, I received an e-mail saying an unauthorised account activity claim was being made. Fortunately, I've not posted the item yet, but I'm not sure what to do next. The resolution centre gives me three options:

1. Item already posted
2. Refund the amount
3. Amount already refunded

I think I just need to refund the amount, however, when I click that, it's asking me to refund the £350 - however, this amount is not actually in my account as payment was held and then removed, so if I select this option, will I be basically giving out £350 for free?

Also, how do I go about getting back my FVF?

Thanks for any help!

This is what my account bit reads:

Temporary Hold To | Buyer Dispute | 15 May 2009 | Placed | Details | -£356.98 | Fee: GBP £14.12 GBP

Temporary Hold To | Unauthorised | 15 May 2009 | Removed | Details | -£356.98 | Fee: GBP £14.12 GBP

Payment From | XXXX | 15 May 2009 | Held | Details | - £356.98 | Fee: GBP -£14.12 GBP