I'm an FFL as are some others here. So who selected the FFL it went to? Before an FFL can ship they are required to have a copy of the receiving FFL's license. If you selected the wrong FFL to send it to then it is your fault, not the FFL that received it. I have had things sent to me by mistake and I usually ask for my regular transfer fee to ship them back, I do not work for free and I doubt anyone here does either. You should not expect the FFL to take care of someone else's problem for free. Is his charge excessive? I think so but that is nether here nor there. You can go ahead and call the ATF, they are not going to do anything since nothing illegal has been done. FYI and FFL can choose to not transfer to anyone they choose not to so watch what you do and say. If I have a guy getting irate over small things how am I to know that he is not going to go postal with the gun when he gets it? And yes, FFL's have been put out of business over that type of thing so it is their prerogative to not transfer.
Just jumping out there and tying to get the ATF involved over a mistake is nonsense. So wo chose the FFL it went to? The seller or the buyer? Who's mistake was it? After reading see it was the buyers mistake. It is your fault, pay the consequences for your mistake and stop trying to get around it. His fees are way high but you made the mistake, not him and not the seller.
Also to add, him keeping it falls under state abandonment laws, it has nothing to do with the ATF. The transfer was done legally so there is nothing the ATF will do, it is a civil matter.