Garden shredder BR5 (St Mary Cray, BR5)

This was bought new and has only been used about 3 times. It seems to mangle the twigs rather than shred them so I don't know if the blade is blunt or it has not been set up correctly at the factory. We have tried but cannot remove the blade to sharpen it. It was bought from Homebase as it was closing so we couldn't take it back.