Because you dont use the recalculate button, that is not what it is for. Recalculate is the most badly named fuction on ebay, it is to revert the invoice back to the original. Simply choose the delivery service, add the cost, preview and send.
Just to add, if you had done a quick search of this subject here on the boards, you would have found the answer. Most questions have already been asked, and can be found if searched for.
