I'm thinking of saying 'even if I did I wouldn't give them to you' when people ask me if there's anything else I can help with at the end of the call
That's very specific, why would you say that to people?
Bill collectors, they deserve to hear those words.
Bill collectors can be demanding when they want the money they have to get from you on the phone. They are only doing their job, be civil and put yourself in their place. If someone did that to you because you were a bill collector would you appreciate it?
OK, sorry..
It's good to apologize and see what you did wrong so that you would have a better attitude towards people and you not being rude towards them will in turn make them more friendly towards you. I hope you be more polite and calm with dealing with people over the phone in the future.