follow up to debt validation letter

I want to thank you for all the advice on your website. I have been fighting a debt for about 4 years it was dismissed without prejudice from court over 2 years ago and new CA’s keep selling the debt. I sent a request for validation letter and was preparing the follow up after 30 days of waiting when a new CA called asking for my addresss. They couldn’t validate so they sold it. I am to my wits end, they don’t own a promissary note, and no CA can validate. How do I get this off my back? Thank you for your time.
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That’s the CA’s little game they are playing and I do not know how to do an end around to stop that.
Sounds to me like you’re doing everything you need to do.
eventually this will stop you would think