Before you try to fix your credit, such as having marks removes from your credit report, it's very important that you gather all of the information about the negative remarks. Start by finding the date that your card was written off by the card company (call the card company for this information), the number of missed payments and any other information pertaining to your accounts. This information may be needed to fix your credit report.
1. Find Errors On Your Credit Reports - If an error exists on your account you can request that the negative remark be removed for providing inaccurate information. This can be as simple as proving the write off date is different than what is reported, or showing that the amount owed at the time of the write off was less than what was reported. This of course only works if an error was made.
2. Request Proof Of The Original Debt - If your credit card was written off there's a good change Citibank, Capital One and other carriers can't find the original billing statements within the 30 days required to response to your requests. If they don't respond in that time the remark is removed as if it never happened. You can also ask for the original contract to be included proving that you opened the credit card in the first place.
Quick Note: Do not simply request "Verification" this just asks that a collection agency "verify" that they received a request for collection on an account with your name. Make sure to specificy that you want actual proof of the debt includes the last several months of billing statements and the original contract you signed to open the account.
3. Pay The Original Creditor - This applies if you have received a letter from a collection agency. Simple send a check with your account number for the full amount to the original credit. If they cash the check you can send proof of payment to the collection agency with a request to fully remove their credit reporting. Under federal law if an original creditor accepts payment for the outstanding debt the collection agency must remove anything they've reported. Sometimes your checks will be returned to you, if they are not returned you can request a removal.
4. Watch For Fair Debt Collection Practices Act (FDCPA) Violations - Under Federal law there are several specific practices that must be avoided by collection agencies. They can not call you before 8am or after 9pm, they can't call you more than one time in a day, unless by accident their automated system calls you more than once, they can not yell at you, belittle you, yell at you or threaten you (I would suggested TELLING them you are recording their calls and then recording them), they also can not send you collection letters if you send them a sieze and desist order, although they can still sue you for money owed after a stop letter is sent. They also can't take more money from your account than you authorize if they perform an ACH and they can't reveal to anyone but you and your spouse (if applicable) why they are trying to contact you. If the agencies in question breach any of these laws you can file a complaint with the company and have a lawyer send proof of their violations while requesting that all debt be forgiven. Typically if they know they had major violations they will pay off your debt for fear of fines up to $10,000 for their violations which they will then have to pay you.
Those are the best legal practices you can take, here's one thing you DON'T want to try. Never use an EIN (Electronic Identification Number) to create a line of credit outside of your social security number, many agencies will sell you the ability to perform this task and it's illegal and can lead to Federal charges.
Good luck and remember to stay persistent as persistence is key in most credit repair situations. Also remember to check all three major credit reporting agencies: Experian, Equifax and Transunion as you may need to rinse and repeat these steps for each report.