Are clothes bought and debts paid with money acquired in a forbidden way considered forbidden, even if one was unaware of their prohibition at the time of acquisition?

As long as you spent the money unaware of its prohibition, you must seek forgiveness (istighfar), cease the act, and resolve never to return to it. You are not required to give out its equivalent amount, and you may benefit from what you purchased with it. As for the debt you paid with that money, your obligation for it has been fulfilled, and you are not required to repay it again.