Same thing happened here - but with a Soccer Shirt from the UK which was a gift for my Uncle last Christmas (eg 2010), I was sent a replacement after waiting 8 weeks, then of course the replacement and the original arrived

I sent them an email offering to return it and pay for the extra postage - they replied saying to keep the extra shirt and thanked me for my honesty

An all round great experience, I actually bought two other shirts from them later as I was so impressed with their service