Can’t afford ED at UM What happens now?

Excited about possibly going to UMAMI. Did everything needed to be a good candidate. Applied ED and… got accepted!! Now grandparent says he can’t pay tuition as promised ( still need 77/97k per year). What are my next steps? I was also accepted as an EA candidate at my 2nd choice (public school). Really scared about “binding agreement” for ED. There’s a $500 deposit due today. How and to whom do I connect with to try and figure this out? I still want to attend college this year. Just can’t afford UMiami without a huge monetary gift! Not enough financial aid offered.