Business Device Activation Unlock

You can call AppleCare for Enterprise and tell them the situation. They will verify the device is indeed in your ABM (and verify you are an admin or device manager) and then they will assist with the unlock. You don't need anything from Verizon.

If you purchased it from Verizon, you need to get the proof of purchase from Verizon.

This is actually incorrect. Apple Business Manager is proof of ownership for businesses and bypasses the need for proof of purchase (Apple School Manager is the same for schools).

In which case, you have a problem. You should have saved the invoices.

That said, if they are part of Business Manager, check in your MDM to see if they are “supervised” devices. If they are, you can remove the lock with your MDM. If they are not, your only hope is to come up with the original proof of purchase. Absent that, Apple can’t help you.

I understand, but if they are part of Apple Business Manager, they will appear as ‘supervised’ devices and the lock can be removed using the MDM without any further involvement by Apple.

If they are ‘not’ supervised, then they are not part of the ABM program.

This greatly depends on the MDM. There are still several that do not escrow the Activation Lock Bypass. A device can be part of ABM and not supervised. If there is a glitch or a reseller is slow to add, the device can still be in there and not supervised or managed. I have an obnoxious amount of these currently...

If the phones are from 2013, it’s not worth bothering with. Anything prior to the iPhone 6 will be completely unusable as a phone by the end of the year.