I fear that if I try your number above, for the other Fort Lauderdale location, they will just refer me back to the FLL airport location. I too would like the extra charge fully refunded, but I feel I am standing on a slightly weak leg having actually signed off on it. It's a salutary reminder to be doubly vigilant the moment I sign something in the future.
Something similar happened 2 years ago at a hotel in England, where the response for an extra night's accommodation was so (deliberately?) garbled that I clearly didn't understand what was said. The next morning, instead of £45 I had been charged £145, and felt really stupid about it. I would like to develop some blanket strategy to deal with sort of thing at hotels and car rental agencies, like asking them to repeat clearly what it would cost or to write it down. The moment you step away from what has been prebooked or reserved, things get potentially dangerous. It's just a reminder to everyone on this forum who actually reads this to be eternally careful when it comes to signing for something.
So far, no reply from the manager at FLL airport, but I think he'll need a bit more time given the time difference to formulate a reply.