我与你有相似的经历 with Sprints。

Right before my contract end, I called them and told them I don't want continue the service. Each time I called, they told me it is take cared. But next time I called again, they tell me I never called to cancel the service. Eventually I have to called my credit card company to changed my card number. Then I called them and told them that I canceled my credit card and not going to pay them anymore. This time they did closed my account.

I heard that Sprints is loosing their customers.

So in your case, just refuse to pay them.