What occupation is the narrator's father involved? (What occupation is Old Medza or the father to Medza involved in?)

We might call Old Medza a loan shark... a money lender.

He jumped. ‘Lord, I’ve got it! You’re Jean-Marie Medza, aren’t you? The son of old Medza, the chap who’s always going round the country collecting the cash people owe him. I suppose that’s what he lives on, calling in loans — everybody seems to have borrowed some off him at some time. He’s a tough creditor, your old man is.