Here's why that $1.50 minimum monthly finance charge is being triggered:
Let say you are going to pay your balance in full, after carrying a balance for some time. Your statement closes on January 1, with a balance of $100, including interest and fees. You get the bill on January 8, and immediately set up a payment online. You pay that $100 in full, and the payment is applied January 11.
Well, you still owe because interest will be charged on the $100 for the 10 days between the 1st and the 11, when your payment was applied/received. So even if you charge nothing the next month, you'll still owe the minimum finance charge of $1.50 for the period between statement closing and making payment. And the next month this could repeat beacuse you'll owe a few days of interest on the $1.50 finance charge.
The only way to get out of this cycle is to make payment in full, including anticipated finance charges for the month BEFORE YOUR STATEMENT CLOSES. Otherwise you'll always owe some minuscule amount in interest, and always be charged the minimum monthly finance charge.
I think in my case, the rep back dated the charge reversals to BEFORE my statement closed the previous month, so that my payment plus reversed fees gave me a zero balance on the prior months closing day, turning off the interest cycle.