returning ipad via ups help

i recently booked my ipad in for repair with apple online. i recieved my packing box on friday, it says in the booklet that ibox the ipad up and but it in the express pak bag with the shipping label on. then it says to drop off the package a t a drop off point or if there isnt on near by to call ups to arrange collection. i have gone to ups online to book a collection but when i enter the tracking number on the slip it says that i will be charged? im a bit worried about this as looking at general quotes online this can range from £40 - £80 !! i thought that apple prepaid for the return? please can anyone help me out.