Sounds like a perception kinda thing might be at play here.
Most likely, the smart customers experienced the increased wait times and lower level of quality service at your SBUX, then said the **** with you and started getting their coffee cheaper and easier elsewhere along with a smile and a hello, how are you today, can I help you?
And that, my friend, leaves only the dumb **** still willing to pay exorbitant prices for good product delivered via sub-standard service with SBUX cards that have a remaining balance on them and those dumb **** have to spend those pennies. Personally, I think they all meet at a predesignated spot, load up in vans and show up at your place.
My customers are always and immediately told what their card balance is and, if any, the amount remaining unpaid. I would never simply say "You still owed..."
Try rewording your response....
Me: Sir, your card balance has a credit of $2.35. The total for your order today is $4.85.
Customer: Ok.
Me: What form of payment would you like to use to pay the remaining balance?
Customer: Oh, there is a remaining balance?
Me: Yes, the new balance due is $2.50 and I can reload your card, if you'd like.
Customer: No. I'll pay in cash.
Me: Ok, you do know you get free internet access while you are here if you maintain a minimum balance on the card and use your card to pay, right?
Customer: I do?
Me: Yes, absolutely.
Customer: Well can I use my credit card to put money on my card.
Me: Absolutely and we can do that right now, if you'd like.
Customer: Here you go, put $20 on my card.
Me: Ok, thank you. Will there be anything else I can help you with today?
Customer: No.
Me: Great, then. Thank you, here's your cards back, and you can pick up your haf-caf, no foam, 3 splenda, small latte at the pick up station and have a great day.
The takeaway:
Aren't you glad I can communicate effectively and express concern that you understand what I already know as opposed to simply thinking you are a dumb **** for not knowing what I know and that I refused to treat you badly because of my misconceptions?
Lord, forgive us when we forget what customer service really means, when we forget that we are stewards of the resources owned by the company and that we are the companies representatives here solely to serve our collective customers and for no other reason, that without them, as we are currently learning, we will not exist. Forgive us as we let the nasty feelings from the cut-backs in staff and benefits permeate our being when we should use those feeling to move us to an understanding of the basic value of the customer to us and the company and our livelihoods. Help us to guard our persona from the feelings of being back-stabbed by the very people we have trusted to guard and watch our tender and exposed backs and help us focus on how we can offer increased value to each and every connection we make with each and every dumb **** customer you send our way and especially those dumb ones you send to connect with CustomersSuckAtSbux--who is having an unusually bad day or help them find a job where they don't have to deal with people, " 'cause dey jus ain't dat gud at it..." Amen.