The point was that an artificial person can't contract, because it doesn't have a mind.
BTW, you entered into what is called an "implied" contract. It just so happens that taking the money....errrr, credit....showed yourintentions BETTER than simply scribbling some letters on a paper. You can always claim that you didn't understand, or where under duress, etc. to nullify your signature. Once you spent the money....errr, credit.... under no coercion, but under your free will, your intentions were known:
You intended to receive a loan, and take that money...err, credit... and use it to give your self REAL goods and services. You intended to exchange future consumption for present consumption. The problem, however, came when the future arrived and you decided that you wanted present consumption AND future consumption....all with no extra labor, no less!!!
"I do not add 'within the limits of the law,' because law is often but the tyrant's will, and always so when it violates the right of an individual."