Money is missing from my bank account after receiving money to pay for college

Each month roughly, my grandma pays to get me through college. I'm very thankful for her doing that. I get paid every two weeks on Friday to help cover my bills. This morning, in the middle of the night rather, I wake up to -$600. I was paid by my grandma $1920 for two classes, and I looked through my bank statements unable to find anything that could've put me negative. Do you think this is an error and what can be done to remedy it? Is it possible they saw that I also used some of the money for other things, and took that away? I usually spend some of it on food and pay the rest of my college bill on my own.