Background Verification - third party vendor is forcing me to give phone numbers of reporting managers

I have recently accepted an offer. As most company does, they will do background check for which they have hired a third party vendor. However, the third party vendor is forcing me to give phone numbers of reporting managers of all your previous organizations.

There are few problems,
1. My current manager has not shared the phone number, I just have the manager's official email address.
2. I am not in contact with all my previous managers. Hence, I do not have their contact details
3. One of my previous organization is sold off, so again no contact details

Does this mean my background will never be verified and I am always at risk of not getting an offer from a good organization.

This is because I am being told that I HAVE to give the phone numbers

If they so insists, why don't you give? After all it is a verification of your past service from your past employers and not like any Police verification. Now a days the organisations hired for doing such background information act like Detectives and the way in which they approach is like an investigating officer trying to find some fault. Let them do their work, of you are confident of your abilities and employability, why should you worry?

Dear Madhu, it is not about that I don't want to give the phone numbers. Neither I have doubts on my capabilities. The question was raised for a practical reasons that I may or may not have the phone number of my manager for whom I worked 15 years back. 15 years a long period.

So, I am not in contact with all my managers, and so I don't have the phone numbers. I have official email addresses. And the verification company is insisting only on phone numbers.