I was promoted into a different unit, do I have to stay the 12 months with them before I can transfer?

CSM William Payne - More than likely, since he didn't get transfer orders until last month, they promoted another Soldier into the slot before he was ordered to transfer there.
Again, improper coding. It should have been coded "vacant, but reserved for a deployed (ADOS) Soldier".

Roger that Top. Bad UMR management.

1SG (Join to see) - correct, that was what happened. When I went to go visit them in person trying to get the transfer done even one of their civilian HR personnel said I wasn't obligated to transfer there since transfer orders wetr never issued, but by that time the transfer paperwork had already been signed off on by my old unit and this gaining unit so it was too late to just go to a closer MI unit. They'd promised to help move my packet forward in tour of duty so I could remain on ADOS orders here at Gordon, but once the transfer was effective I got almost zero assistance from them with getting my packet finish in tour of duty and the last day of january HRC decided to stop extending my orders while we tried to finish getting the tour of duty packet finalized so over the weekend I found myself suddenly off orders with no time to demob. They didn't respond to my emails or phone calls until mid-february, which has sort of given a bad impression on how I can expect they'll take care of me if I'm forced to stay there for a year before transferring back to an MI unit.

SFC (Join to see) - I'm speculating here, but I would guess that someone in your CoC is hostile to you being on their UMR and on ADOS orders. This happens a lot. There was probably some internal deliberation going on, hence the non-responsiveness.
Guessing further, they're probably going to play hardball until you report and put a human face on the issue with actual leaders, not just the UA. Figure out what tack you want to take (hint: don't use sympathy. They won't have any.) and give it your best shot.
If they say no, you're stuck unless you want to risk the promotion being revoked and them collecting all of that E-6 pay if they're really feeling vindictive.
If you are destined to remain there, win them over with your qualities as a Soldier. Right now, you're just a name and an SSN on the UMR. Make them see that you are more than that, and readdress the issue again down the road.