Hi Darkleafar,
Unfortunately Angelbeds is now out of business so there would no longer be a valid warranty on any of their mattresses and their customers no longer have any warranty recourse if there is an issue with any of their mattresses. One of their founders is now involved with a new company (see post #4 here).
I don’t know if you would have any legal recourse (although it’s unlikely) but you would need to check with a lawyer for any legal advice.
I would check the foundation under the mattress just to make sure that it isn’t the reason for the “caving in” (you could also put the mattress on the floor to see if it makes any difference) but if that’s not the problem then outside of purchasing a new mattress the only other suggestion I have that could help would be to do some “mattress surgery” to identify and replace any of the defective layers in your mattress (see post #2 here).
Phoenix