This type of debt slavery is not like the slavery of the blacks. For example the owner was forbidden from any kind of corporal punishment, the slaves ate exactly the same food as the owner, and their beds had to be at least as good as those of the owner.

You couldn't leave, and the owner got to choose your wife for you (if you were not already married), so it was not the same as freedom, but it also was not the same type of slavery you are probably thinking about.

There was a whole procedure a slave had to go through if he voluntarily chose to stay after 7 years - not something you would expect if it was the severe punishment you are thinking of.

There was also a concept of war slaves, which was different from debt slavery.