MSU took away my Pell grant

I took a summer class earlier this summer, I was enrolled in a 3 month payment plan and payed it all on time, which was already so much for one class, received ~900 in Pell grant and had 500 remaining for the class. My last payment is due 8/1 and I open my student account, and they took back the 900 and charged a fee as well. I now owe 900 than I was supposed.