If you are getting a collection letter, then most likely the information has already hit your credit report.  However, you can try to reduce the damage by disputing like you already have or fighting the collection effort.   You note that you have already disputed the account.  If they cannot validate the debt, then you should notify any creditor reporting agencies that they have refused to validate the debt.  In addition to disputing the debt through the collection agency, dispute the debt through procedures for credit reporting.  Most major credit reporting agencies will include a dispute form or process when they send you a copy of your report.If the collection agency does validate the debt, then your main remedy will be to fight the charges associated with the account.  Your lease agreement will control the extent of your remedies.  Even if the leasing company can charge you for the balance of rent for the apartment, they still have a duty to mitigate their damages.... and charging you $8000 does not sound like they mitigated very much.  Once you get the validation paperwork in from the collection agency, take that paperwork and the lease/rental paperwork to an attorney.  Try to find one that has experience with contract, consumer, or landlord tenant law.  If you are able to win the suit, then the collection agency has a duty to update the information that they report to the credit reporting companies.