That's because I had absent-mindedly paid it twice last month, and my bill said I had a balance of -$111.86, i.e., they owe me.
I explained this to the lady, and she said I still had to make a payment. So, I just did an online payment for $1.00. It probably will cost them more than that to process it.
WTF???? Calling and harrassing people to pay money who don't owe it to you? Is that legal??