The monitoring station is ADT so there is no way of cutting out the middle man, you cant go directly to an independent ARC either they will only deal with trade, and even so you would need someone to program your signalling unit. I would advise before you do anything rash that you read the small print in your contract carefully, you may find that you dont own the control panel and changing companies could end up costing as much as you save, as norm says it is worth going back to ADT saying that you are thinking of moving, this works with Virgin and BT so I see no reason why it should not work with ADT.
I used to hate ADT with a passion, but as the years have gone on and chatting with the ADT chaps on here I have a lot of respect for them, its not them doing it wrong its everyone else, providing quality security with qualified staff costs money and their charges reflect this