I had exactly the same thing happen to my first frame, the frame builder I took it to to ream, face etc claimed that it was so far out of alignment that it wasn’t his fault. This was b*ll, as he checked it over when I dropped it into him.
I ended up replacing the tube (down tube) it was a lugged frame so a real bitch of a job. Ben, I think you contributed to the thread on the velo salon forum. I bodged it and whilst not pretty I have since ridden it for 1500 kms and it’s still holding, but number 2 is approaching completion and I’ll be buying the tools to finish it myself.
In your case, I’d try the tube block approach, the seat tube is less stressed than the down tube in my case and I had a pretty serious crease, which defo wouldn’t pop out.
I learnt a whole load about frame building from replacing that one tube, the most important lesson being to be self sufficient and save for the right tools!