Disgusting service no exchange

Today I went into Milton Keynes jd sports store I wanted to return a pair of Adidas trainers which I purchased on 31st January 2013. I went to the desk and the member of staff was so grumpy aswell as all the other staff and he said I have to wait for the 'one' manager to authorise if. I waited almost 15 minutes and the manager turned up all grumpy and didn't even bother saying sorry for keeping me waiting. Then I showed then that the trainers had start to come apart on the side and my brother only wore then once a week as he goes school every day. They said they can't offer an exchange as its over their 90 day policy which doesn't say anywhere on their receipt of anywhere in the store
And I said to them so your telling me all your shoes you sell here are only supposed to last someone 90 days
It's absolutely stupid. I paid £45 for the trainers I expect them to last at least a year as my brother only wears them once a week.
Absolutely rubbish customer service, the staff are so rubbish too
The managers think they have some high class job and think that if they are bring polite they are not doing their job properly
I would never recommend anyone to buy trainers from there!
Disgraceful service!