I am so sorry this happened to you I can't believe they would send out the letter of acceptance before reviewing your GPA? Is there any way you could contact the person that interviewed you and tell them circumstances have changed? Wishing you all the best
3.5cgpa 3.8 last 2 years (first year amirite ><), 2 years working full-time in public health, 3 years as an RA in public health and health policy fields