The reason ATP can’t use your GI Bill is that ATP is not a Part 141 school and the govt will only cover Part 141 schools. The reason ATP is Part 61 (vs 141) is there’s no way ATP could offer their accelerated curriculum under the very “time specific” FAA requirements of Part 141.
As for advice I’m not sure what you’re asking? You say you “chose to continue with Spartan” which implies you’ve started and are training with Spartan which is fine. I’ve never been one to second guess a decision after it’s been made. My only advice I have is study and work hard. Good luck.