Main beam wont go off

Hi I have had this prob for a while now but the lights wouldn't come on. Every now and again they would come on by them selfs but not go off. Until I turned lights of now they won't turn of even when engine is of and key removed. I've pulled the fuses to the main beam.everythng else works fine .e.g dipped beam indicators fog lights. I've done research and believe its a faulty com 2002 unit. My question is could it be anything else and if replacement is needed do I need the exact same part no as I believe there are many variants of the same part. Any help would be greatly received thanks