Did you open a claim before the seller refunded you?
Normally you would open a return request since you were sent the wrong item and when the seller refunded you through the case, the gsp would refund you the import fees and international shipping. The gsp refund isn't always instant but it is automatic in that situation. Bu tif the seller just refunded you on their own I'm not sure if that alone will generate the gsp to reimburse for the amount owing. You might have to contact customer service and explain the problem.
Try contacting customer service on facebook or twitter. You can send a message with the information about the transaction and they will reply back.
https://twitter.com/askebay
https://www.facebook.com/ebay/