only problem is the store is like 45 mins to an hour each way from me so will cost me about a tenner in fuel to get up there any back. How much would a bike shop charge to have a look at it do you think? as to be honest they have already lost all the confidence that i had in them.... not even pumping the tyres up is just not acceptable
I can almost guarantee if you take it to a local store you'll be told it is a piece of cr@p and you've wasted your money. This will simply be untrue.
Remain firm in the knowledge that you've bought a decent bike which is badly adjusted, smile sweetly, and just keep saying "Yeah, I understand but how much to sort the gears out?" and I'm guessing you won't see much change from £20 depending on the attitude of the shop who may simply pick holes in it and 'fix' things that don't need fixing and charge you twice that.
So a trip back to
Decathlon to talk to a grown up is double plus good because
It's probably cheaper
It makes it, via your polite but assertive complaining, less likely that the next customer will get sold a badly adjusted bike setup up by spotty yoof
you'll feel better about your bike and about yourself.