You parents are the ones that decided to have the children, yeah?
Why, then, are you burdened with costs because of their decisions?
This is exactly why I don't want to have a child, because they cost money AND you're making the choice to bring another entity into the world that will have to deal with the same bullshit that we do.
Back to topic, my father gave me an ultimatum for when I graduated from university: six months of living at home in order to find a job.
Instead, I moved to Taiwan three months after graduating from college and having been paying my own bills ever since. It's much easier that way, I think. Family billing and lending, in my opinion, complicates matters.
On the other hand, my girlfriend and her three sisters, well the ones that still live at home, pay rent to their parents. Now, this is an Asian family, so their cultural standards are a bit different (like being expected to live at home for a long time). She doesn't seem to mind and even came up with the notion that she and her sisters should pay for the Internet, as well.
So, I guess if you're trying to be super nice to yours parents, you could pay rent. But, it seems your mom owes you money, so I'd say that, first, you get seven months rent free.