I have 3 sets of headphones, being he exact same size. They all fit and even click into my old phone's head jack, where as with my new phone the lg optimus g they go in midway and the only way for the headphone jack to read the headphones I have to hold it in. There isn't dust in it or anything I don't know what is happening. This is ridiculous
Take it to the shop you bought it and get them to work out what's going wrong. This isn't the sort of problem you can easily fix over the internet: you need an expert there to see what's up with the jack. In addition, if it's a common problem, the people at the shop will already have heard about it from other customers. Maybe the jack is just too tight and needs some more force, or maybe there's some fluff stuck inside where you can't see.