You cannot pay a cost you impose on others with self induced suffering. I cannot steal and break my own toe to "pay it back". That justification is nonsense.
Orwell is saying that to see someone suffer is in line with our ethics; someone who suffers can be ethically reasoned to have earned what dues come their way.
Compare the beggar in orwell's quote, if you will, to the injured war veteran who benefits from a fundraiser. He has suffered, so we consider it worthy for him to benefit through community actions.
Why is he worthy of the benefit? Because he suffered. I am not worthy because I have not suffered as he has. The beggar? Suffering.
You are thinking very stringently if you are interpreting the quote as a 'literal' trade, broken toe for dinner for a week
The injured war veteran, at least according to the official fiction, suffered in the course of benefiting the community. Whether they succeeded is up for debate, but the intent to benefit is seen as evidence that gifts/support/etc. won't "enable" them.
The beggar provides value by only extracting a pittance. If he were, say, a burglar, he would be taking far more than he needs, and that would actually be costing you something less reasonable.
If everyone only used what they needed, we'd all have plenty of resources to dedicate to the communal good.
In which direction? Is it because the veteran is a murderer while the beggar is harmless or because the veteran's suffering is more severe than the beggar's?