So let's imagine that you move into an apartment and want to get broadband/cable. And let's say that the previous occupants of said apartment weren't so into paying their cable bills. They've paid off a massive chunk of it, but they still have a way to go. Captain Clever of the cable company decided that the deal in Madeira would be that the new person stands the debt until the welchers finish paying it off (and we all trust that the welchers will pay). Then when they settle their debt, the new person is refunded the money they should never ever have had to pay in the first place.
A truly bizarre system. Surely an easier way would be to cut the welchers off after a few months. Achieve some closure.