I've tried logging in, unlinking, and removing the game from my Steam Library. When I initiate a new PCMove, I see the correct information with my purchases and my characters and the option to begin the transfer. When I click that button, the[ pop up (https://cdn.discordapp.com/attachments/287117328657940480/630167364276715530/unknown.png) appears for less than a second before it reverts back to the wrongly associated Battle.net account. I can try again, but each time I try, it pops up for a moment and then reverts to the wrong account. There is no time at all to click on the "Continue" button. I am at a total loss.
PC Migration is a one-time process. Since you already performed the action involving that Steam account you can longer use that Steam account for a subsequent migration.