How does a credit agency get validation?

I have an entry from Capital One on my credit report. I don’t recall ever having an account or card through Capital One!

I sent them a letter, asking for more info. I gave them my name, current address (I had moved within the past year), and account number as it was listed on my CR...wasn't the full number though (that's how Trans Union had it). I mailed it CRR to the address as listed on my CR.

Their response was that they could not locate my account. They asked for my social security number, date of birth, former addresses, current and previous employer’s names, etc. Hesitant to provide such personal information that I do not recall having business with, I ask you guys advice and was told I should not contact them further, rather I should dispute it with the credit agencies and have them validate. I will be sending them a letter this week.

My question is, when the credit agencies seek to validate, how do they do so? Will they be providing my personal information (SS#, DOB, etc.)? I really don’t want this information shared with a company I am unsure of having business with!!!!

Thanks!