First, read the warranty booklet. In the US my book states that "wear" items, including wiper blades down to a light bulb are covered under a 12 month/12,000 mile warranty. Unless the dealer can prove abuse or mis use of the vehilce, I would say they were obligated to repair the problem at Kia's expense.
In the US Kia offers a 12 mo/12,000 mile warranty on wear items which would include alignment. This warranty would not cover mis-use or abuse of the vehicle, so if the Sorento has been in an accident or shows signs of serious off roading they would not be obligated to honor the agreement. Another possibility is a sticking brake caliper on the side of the pull.
My Isuzu went back three times for alignment in the first three months at no charge. But to this day, and I now have 70000km on the clock with the original tyres, it still pulls to the left. I was told that it is caused by the tyres. That was confirmed by two independant tyre dealers. I rotate my tyres every time it goes for a service and there are no signs of unusual wear, despite it pulling to the left. I need to replace tyres soon, hopefully that will sort it out? I hope to sell it though and buy my Sorento before I have to replace the tyres.