What can sometimes happen with these is that you get a build-up of coffee under the basket that glues it in place.
You might try soaking the handle in warm water overnight and using a screwdriver to pry it loose.
If it is really bad you may have to tear the basket apart and just replace the basket. You can purchase replacement baskets online.
You can also send the group handle back to our service department and we can replace the basket for you.