cancellation

OMG... I could scream, I made a sale last night, this morning the buyer requested to Cancel which I did straight away. this afternoon I have checked  the details and the buyer has been refunded but because I pay the postage ...although haven't taken the code which then would charge me I have been charged and not refunded. I have been through every page and option to find out how I get this back including so called chat, what a complete waste of time I am no wiser, can anyone advise as I have never come across this in 18years ...Thank you ..