How do you get the collector to respond to your dispute?

The best way that I have found to do this is to send every letter registered mail so that they have to sign for the letter. This way you have proof that they have received it. The collector has to investigate the dispute within 30 days of receiving your letter, if not they are in violation of the fair debt collection practices act and you can sue them. If they fail to respond, send a letter directly to the credit reporting agency (i.e. Trans Union, Experian, and Equifax) along with copies of the proof that they received your dispute letters. They should directly remove the item from your credit report.