Just because a business isn't licensed in the state doesn't preclude them from seeking to collect debts owed to them in the state. Cach is a large debt collection company and is licensed as a debt collector in Nevada. Are you sure they aren't also licensed as a debt collector in California? They do not need to have a business license or have a physical presence to be licensed by the state to engage in debt collection. Hope this perspective helps!
What you would put in your Answer is called a "Plea in Abatement." You can allege this. If you can prove it, the lawsuit may be delayed while CACH complies with any legal requirements that it failed to do. You should review California Corporations Code section 191.
CACH is usually represented, in California, by Neuheisel in Sacramento, the Briesmeister office in Montclair or Russell Davis in Solana Beach. They have dealt with this issue before.
You should have an attorney review the entire case. This one issue may not be dispositive. Does the underlying contract include an attorney's fees clause? If so, and if you win, the other side may be responsible for paying your attorney's fees.