There shouldn't have been /any/ debt after WWI (except to Belgium, who didn't ask to be a battle field in the self defense of Germany).
Russia, France, Britain, and the US should have paid reparations to Germany, not the other way around.
Why? Because Germany /didn't/ start the war. It just ended up as one of the losers.
Germany had huge territorial losses after both wars, parts of Germany were under forceful occupation for a long time afterwards, and they paid heavily in terms of manufacturing equipment and money afterwards. I'd say they paid.