Sons verizon wireless charge off on my credit. Disputed this collection.

I have a problem, I have done almost everything I am suppose to
Pulled credit reports
Disputed for months, sent certified everything, kept copies kept detailed records, now I feel I need to send letters of dept validation to Verizon (1999) I have already disputed this with the 3 credit ber. of course they came back valid, these are my sons acct (they merdge the two accts SR and JR, when I ? this they just put a fraud alert, my ? is do I send Dept validation letters to the collection agency, or to the credit beru. or both ? thanks in advance. this is like a part time job
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send validation letters to creditors (verizon)
they have to confirm the information is correct and legal
Some how they must have you ss #
your son might have given it to them? I do not know
validation should clear it up
if they just verify who you are and your address
send the follow up.
all certified mail