As for the letter you just got you need to see if it is reported on your credit report by the collection agency. If not I would pay it in full as fast as you can to the OC and dont mention that you have received a letter from the CA. Then you can DV the CA and state that it had been paid in full to the OC before going to CA. or you can contact the OC with a PFD.
As far as the DR bills if you want to pay them you should probley not make them wait much longer or you may not get any help from them.