If the matts are going to be hard to get out, it might just be best to splurge and take your rabbit to the groomer this one time, and get his coat shaved shorter to get the matts out. It can sometimes be hard cutting out matts with scissors, cause if the matts are close to the skin, you don't want to accidentally cut the skin with the scissors. You could also buy your own set of dog clippers, and do it yourself, if you think you are going to have to clip his fur very often. Just be ready for the sound of clippers to freak your rabbit out, and make sure to have a good hold on him. It sometimes helps to cover their eyes with a towel or something.