I had enough of straight talk (dropped calls, no internet access even though 3G connected, no service in weird places) and moved to Verizon. Moved my number and clicked 'cancel service' on their site. Got billed two more cycles, called them, took forever to get sby on the phone. They finally told me that I did didn't stop them from billing me (even though I had no number or service). To do that I had to both cancel online and call and have my account stopped. Escalated, twice. Talked to a lawyer. Talked to them. They finally took the charges off.
Moral: you're going to 'pay' one way or another. Either out your wallet or up your ***.