Take someone BIG with you when you go in to complain. Tell them you know your stuff and you know that the other tyre was fine and you want to see it. Take a look at the pads too as they said they needed doing. If they don't, go back in the same car and ask them to show you why they need replacing. Be firm but not aggresive and ask to speak to head office if you get no joy. The longer you leave it the harder it will be to get any joy from them. Good luck with whatever you do mate