Charge for no Service

I cancelled my alarm after 12 years with ADT due to the fact we sold our house.<br> I informed them on the 17th of Jan. They said I should have given them 30 days' notice. I still get charged for the full month of Feb. Although I had no service from them in Feb and the phone line was also disconnected on the 31st of Jan. Well ADT for 12 years you took my cash, I will never ever deal with you again in future. I am also telling every person I can about your bad attitude, and when I escalated the problem, you also did not bother to contact me back.