Unfair billing

On the 10th November i cancelled my contract with ADT due to a terrible and unprofessional experience, I was told that a technician will have to come and remove the radio and aerial and then give me a installation code for my keypad at my cost, which I then had the new security company to remove the radio and aerial and they reset the keypad so I didn't need ADT's assistance as they kept saying someone will have to come out for this, all this was done without extra cost to me. So by the 17th November ADT had collected their radio and aerial yet I have been charged a full month for December even though I can't make use of their service??? I feel that ADT could at least work out a daily rate and charge me till the 10th of December keeping it a 30 days notice period. I asked today that a supervisor call me as i was getting no where with the consultant which i am still waiting for this call. I think my frustration is that if we are being billed for the month ahead and their equipment was removed on the 17th then in fact they want me to pay for 7 weeks of no service because I have to give a calendar months notice!!?? This is unfair.