I'm so sorry to hear that you lost your job there, but perhaps it was simply for the best. You can't be "too nice" to be a bill collector. You have to be tough, mean, aggresive, and a bser.
I know myself that I would not last one day as a bill collector. I am not only too nice, but I'm a very sensitive person; especially to people who are in financial trouble. I would simply say to them, "Oh I'm sorry to hear that." or "That's allright. Just pay whenever you can."
I hope that you'll be able to find something that suits your personality. Being a bill collector just isn't for everybody.
Take care, good luck, and Happy Holidays!