I am not for a second doubting you because you wouldn't have posted here unless you truly had completely run out of money. From your work's point of view though, it is extremely rare to genuinely be down to your last penny. I can understand why they are doubting you and you will not be entitled to pay for today and also risk disciplinary action, though this will be up to your employers. How far away is your work?
Do you know when you will be paid? Have you got enough food until then?