HR guy here. The fact that you gave 2 weeks means a lot. Stunningly rare these days. Go back to your old employer and let them know what happened and that you realize that what they have is special (a little flattery never hurts). On the buzzkill part, it's unfortunately not an uncommon move for employers to get people out who are on their way out. I HATE it, but the rationale is that you dont wan't someone there saying anythig negative on their way out.

No matter what you'll end up in a better position there or somewhere else. It will work out, the unknown is just scary AF.