If you didn't ask for NeverLost and they gave it to you, they should not be charging you for it. You were right to stick to your guns and demand that they take it off. It doesn't matter if you reserved a B and got a Audi, you pay for what you reserved and in your case that is a compact car and not a Full size with NL.

For future reference, if your protest at Hertz in MHT doesn't work, you could email Hertz CS and have it taken off your bill.