How do I get this off my credit report if they wont respond?

What is the date on the claim on your CR, has SOL expired? i would dispute this on your credit report once again. You also may want to send a valdation letter to the collection agency

Go to this link for the address of Rossman & Co. Send a debt validation request so that you get their genuine purpose of reporting in your file. If their reporting is correct, the information will be put in writing. If they don't respond with a reasonable time period, send a follow up letter and request for the same information done earlier. Send a copy of the previous letter with the date in it. You should expect a reply by that time. If they don't, dispute the item with the credit bureau and send a copy to your attorney general. Give it a legal importance so that the matter is taken seriously. No incorrect information should stay in your credit file. Don't let the incorrect item stay in your file for long because your credit is getting hurt.

Send all your letters through certified mail with return receipt requested. Keep copies in your folder so that you can prove your actions at a later stage.