Go to your orders dashboard and on the left hand column you will see "postage lables" Find the one and on the edit select VOID LABEL - then purchase another label, You will unfortunately have to wait for RM to check that the label isnt used so think its about 5 days then they will refund. Before you do that though check that this buyer doesnt live somewhere Evri dont accept (or charge a fortune for) typically Channel Is, Scottish Is etc, which is why the system may have defaulted to RM