New to this and freaking out...

I currently have 3 CA's calling me. I have avoided their calls assuming they were CA's until the past few days. I answered, didn't give them much and got the account numbers (they tried to only give me the last 4 until I specifically asked for the entire number), amount owed on those accounts and who the OC was. I don't know what I should do. I do not have the money to pay or settle them. I know I can send out a DV letter. The thing with these CA's is I have not received one letter from any of them. I have had to move multiple times this year for various reasons, so maybe they sent them but I haven't received one. I don't think they have my address now because while speaking with one of them he went over my previous addresses and when I tried to give him my new one he kept cutting me off.

Also, can an OC and a CA both have reports on my CR for the same debt?

One other OC has a CA but I haven't been contacted at all. Should I send them a DV to get this out of the way?

Please, can someone lead me in the right direction???

Krystal