Out of state Dulles Greenway toll

Looking for some advice from anyone who's dealt with the Dulles Greenway toll payment system.

I'm a ex-NoVA PA resident with a PA E-ZPass. A few days ago I received a toll notice even though my E-ZPass was working. I disputed it and provided proof that I had successfully used the same transponder minutes before on I-66. The Greenway acknowledged there was an issue at the toll gate and waived the $25 administrative fee.

I'm happy to pay the remaining $7.80 toll, but they say it can't be charged back to my E-ZPass account and must instead be paid through their payment portal. The problem is that every payment option carries a mandatory $1.99-$2.99 service fee, and they no longer accept checks.

It doesn't seem right that I have to pay an extra fee because of an issue with their equipment. Has anyone dealt with this before? Is there another way to pay with no service fee?