Vector Security Won't Stop Service Columbia, MD Nationwide

I signed a contract a few years ago and had been waiting for it to end because we rarely used it.  I called to find out how much it would cost to end the service, and was told that my contract was over in July.  I was provided an amount to pay and paid it.

While painting I somehow activated a sensor.  I thought the service had ended, and was told that they hadn't received written notification - and now we owed another month? 
 
1) What was the sense of me making a lump sum payment - other than to end the service?
2) I didn't keep a copy of an agreement, but remember it was for either 3 or 5 years - not for life. 
3) What other home consumer service requires written notification?  Phone, Cable..... what non-sense.
 
I honestly had nothing good or bad to say about Vector - we just didn't use it.  Certainly doesn't seem right and out of general business practices - just another way to get a few extra bucks and make the consumer feel abused.