if you bought it online and emailed them to tell them you didnt want it FOR ANY REASON within 7 WORKING days and you live in the uk you are entitled to a refund including a refund for the postage, even if you unpacked it ect. as set out in the gov guidelines below.
oft.gov.uk/shared_oft/business_leaflets/general/oft913.pdf
it dosnt have to be faulty, you just have to not want it anymore. they should even pay for the return of the item to them - hope this helps, it is the law, you should forward the link to them if they still complain.