I have received the full amout I paid for an item instead of a postage refund. How do I rectify this as the item is now in my possession.

[janc103]

I paid for an item and the seller refunded me an amount of $3.05 for postage difference.  Instead of receiving the $3.05, I received a full refund of the $30.00 I paid. I have received the item in good condition etc. How can I rectify this.  I have contacted the seller and am waiting for a reply.