That's beside the point. As the linked thread makes clear, by requesting arbitration, you will get someone competent at Hertz to look at your situation quickly and try to resolve it without actually going to arbitration -- which would cost Hertz thousands of dollars in fees.

You've tried to resolve this issue by the normal channels, but your submission to Hertz went unanswered. And Hertz is still pursuing you for the additional money.

The only unknown is whether, as a UK resident, you are entitled to avail yourself of the arbitration option.