@lisainden thanks for bringing this up!
I think collections is such a difficult topic... We're not used to having to deal with it. I agree with all of the above and would add that it helps to have a standard way of discussing it so you don't have to think of it. I always send a portal message saying
Subject: New Card?
Message: Dear X, It looks like you might have a new card. Would you please update that under "Payments" so we can keep your account up to date? Thanks so much!"
And if they are in the office and behind, I always say, "Oh, I see your card isn't running. Do you have a new one that I can enter for you while you're here?"
Every so often they say there isn't any money there and ask me to change the date to coincide with their paychecks but most of the time they complain about getting yet another new card.