When you buy something as an individual i.e. not for your business, trade or profession you have certain Consumer Rights. Citizens Advice Bureau give excellent advice on exercising these rights on their website www.citizensadvice.org.uk. Just go to the advice for the relevant country and type in the item you are having a problem with. They have all sorts of resources on the site including letters of complaint. I hope you find it useful.
(July 2016 Question 2)