Sounds like you're actually in a good position since no one can adequately verify the account, particularly the 3rd firm who has no records.
If I were you I'd DV the company listed on your CR using CMRR. As soon as you receive the GC back then you should dispute with the CRA. Since no one can provide the required documents to validate the debt it should be deleted from your CR.
Sounds easy, but it may or may not work this way. Keep your fingers crossed and let us know what happens if you decide to go this route.