OAT doesnt lend anyone any money, HSBC does. As Blinkz said, they are a company, and are there to make money. Whos money you come to them with doesnt matter, but you have got to come to them with it all. Just because you have passed the selection doesnt mean you are guaranteed a place on a course, a cheque does.
I know it is unfortunate if you cant get the full loan and you need to but thats the way it works. You just need to drum up the cash. They may have some special cases though, you could always go and ask them?
Good luck though with it link4!