GMB Verification Issue

I have a verified GMB location in a city, although it uses a mailbox office. Recently, I wanted to create more SaB listings, as most of the competitors within my industry do that. Started with a single location (different city and the name is styled like ' [Name of the company] - [New city] office ' and the postcard was sent to my verified GMB listing.

Now the tricky part comes in. I got the verification code for the SaB listing, but my original listing got marked as duplicate. The new location showed up instead. So, I followed Google guidelines - removed the listing that I don't want to keep from my account and the location I want to keep will show. This didn't happen.

Contacted them, and they tell me to send a front picture of the office. But my location is in a mailbox office, so I don't have any logos or names.

Any thoughts on what I should do?

they also offer the option to verify by sending them a video where you show them documents that prove the location of the business: utility bills, bank payments, invoices, contracts.