Do they have 30 days to respond or remove clean delete the bad credit

Bo after the company receives your letter they have 30 days from the date of receiving the letter to validate. If they do not what should I do next.
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what company
what letter

if you dispute with a major credit reporting bureau the bureau sends the dispute to the account holder who then has 30 days to respond.

if you are using debt validation you send the letter to the account holder and they have 30 days
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If it an account validate to collections company. If they do not respond in 30 days what is the next step?
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send the debt follow up letter
make sure you send the letters certified delivery

if they do not respond, then use the dispute form

if nothing seems to work call your state attorney general or file an online compliant about illegal use of your credit report.