Why did you expect a large package from a school that does not guarantee to meet need? Just because you filled out a FAFSA (Free Application for FEDERAL Student Aid), does not mean that the schools have to give you a large package or a full ride. Those are rare!
You said that you were eligible for the maximum aid possible. Well, that maximum aid was coming from the feds, not the school-Pell is $6K. BU is a private college that does not guarantee to meet need. BU is known for limiting funding.
The Feds can only give you so much; the rest has to come from the schools where you apply.
Typically, the best aid comes from university dollars, and a university can and does run out of funds.
Get your deposit back, and go to another university that you can afford. You shouldn’t have deposited without knowing what your full costs would be.
You can’t “demand” an explanation; that’s just very rude and shows that you didn’t do your research. (Private college that does not meet need-NPC?)
If you caused a ruckus, and started “demanding” action, they don’t have to lift a finger to prioritize your funding.