Economic Slavery has always been there and is still there. There are plenty of jobs which people don't want to do unless they are poor. Either countries kept parts of the population always poor or imported from poor countries. Like mexicans in america. Exploiting the working class is a feature of modern variants of capitalism.
Legal slavery is the only thing that got abolished.
P.S. on a seperate note and no means a defense of this, the salary is slightly misleading as it usually includes stay and food.
What sounds particularly indicting in the described situation though is employers keeping the employees' passports. Things like this can make someone's situation more similar to a slave's.
I am not sure there is all that much difference.
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Its not quite so simple though. By that definition migrants from Eastern Europe working farm jobs in Western Europe are economic slaves, but their conditions are much better than these maids and they can go home anytime without repurcusions.
During his lieutenant-governorship, Raffles placed some restrictions on the local slave trade in line with wider British policy across its Asian territories, although slavery remained widespread and Raffles himself was served by a large retinue of slaves at his official residences in Java.