If it's a kitchen table FFL, follow through with whatever CDNN offered as assistance.
If it is a brick and mortar store, pay them a visit.
I had a dealer hold half a dozen AR lowers for ransom, after they were in his possession, a few years back. (He "changed his mind" from the agreed upon $40 transfer to triple digits.)
I called Tennessee Arms Company, the company that had shipped them, informed them of the situation, asked if they might be able to help, and then gave them time to work out any possible solution from their end.
I don't know what went on between TAC and the FFL, but I later got a phone call from a person very much in agreement with me that the FFL was a dirt bag that the company now hated as well.
TAC shipped replacements to an FFL across town, and told me that they would blacklist the dirt bag FFL and "pursue the situation" from their side to get their lowers or a refund.
They took control of the situation for me, just to ensure that I was a happy customer - even though it wasn't their fault!
Unfortunately, I later had to go through a very similar situation with an FFL that shipped an AR lower without asking me which local FFL I wanted to use. He just picked the only "gun store" hit in his Google search, and sent it to the dirt bag FFL. ...But that's another story.