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This is as much for your own records as it is for making sure the account is closed. Sending a letter will finalize the closure of your account and give you a legal written and dated record of your action should anything go wrong with the closure of your account. If you really want to guarantee full legality, send the letter by certified mail and hold on to the receipt you will receive upon paying the certified postage.  In your letter, request written confirmation that the account is closed. Make sure to also include your information, like your name, phone number, and address. You may also want to include proof of payment from when you paid off your remaining account balance. Do so by including a cancelled copy of the check.  You can also request that your credit report say that your card was closed "at the consumer's request." This will make the situation clear to future lenders. Make a copy of the letter and keep it in a safe place. By doing so you will have complete and reasonable proof that you closed your credit card account. Also be sure to hold onto the certified mail receipt. This will help prove that the credit card company received your letter. Follow up a few weeks later to make sure that your account is indeed closed. Companies may occasionally make mistakes and fail to close your account. The closing process can take up to a month, so don't worry if it isn't closed after a few weeks. If your account has not been closed after a month, though, it's time to take action.  Once closure is confirmed, cut up your credit card to finalize the closure.  You can check whether or not an account has been closed by obtaining a copy of your credit report. Check your credit report a month after you first called to have your card closed. If the card is still active, it is is time to take further action. First, try calling your credit card company again and writing another letter. Wait for a response. If this fails, you can file a dispute through a credit reporting agency (either Experian, TransUnion, or Equifax). Each agency's website has clear instructions on how to do so. If your account is still open after this, you can file a complaint with the Consumer Financial Protection Bureau at http://www.consumerfinance.gov/Complaint/.
Write a letter to the credit card company reiterating your intention to close the account. File the letter in your records. Wait a few weeks and then contact your lender to confirm. File a complaint, if necessary.