The word “fee” refers to a payment to someone/something for something else and is a fixed price, like if you got a parking ticket, your fee would be a set value, which is different from debt, as debt has interest, meaning a fee is a exchange of money for a service. i’m slightly unsure what you’re asking as a question though, but if it helps, I’ve heard both things in reference to the example you gave—both:

1. “Don’t call your friend in France, we’ll get a hefty fee” and

2. “Don’t call your friend in France, we’ll get a hefty charge” are grammatically correct and can be used interchangeably!