Sprint PCS (Poor Customer Service) THEY KEEP BILLING ME EVEN WHEN SHUT DOWN TWO MONTHS AGO! Internet

Today I received a bill for long distance service from Sprint. I changed long distance carriers two, possibly three months ago, and Verizon said they would contact Sprint to shut the account down for me. When I received bills I called Verizon and encountered a nasty man saying that only third parties can turn off the Sprint account. Then I called Sprint and they said they have not received any order from Verizon, and I was assured that the account is now closed down. So here it is another month and I am still being billed by Sprint $8.64 - now at least $26 over what I should be paying. The reason why I went with Verizon was to close down an account I was being charged for which I never used, and now insult on injury am being billed double usage (by two companies). I called today and was assured (again) that I would not have to pay another amount by Sprint - and I know this is not over. Does anybody have any suggestions on how to handle a company that keeps billing regardless of what one does given their remedies and poor customer service? Does any corporation even understand the idea behind customer service and actually give people what the name implies?