Maintenance loan changed

My maintenance loan was granted for £6600 initially for the course that I choose first. I changed my course last week but with the same university and at some point i saw today that my maintenance loan has been reduced and changed to £4400. I am doing a full time course and staying in halls of residence which costs me about £7700, as I did not get any room lesser than this. I was wondering what is wrong here? why has my maintenance loan payment changed. I am really worried about this as I cant make extra £3300 to pay. Please advise.