is it reasonable to charge the service for removing the firmware password?

So this was an independent repair shop? Even though they are an authorized provider, they can set their own pricing. They are not obligated to charge what Apple charges. For example, I had a phone where the battery was going to be replaced with a small "service fee". The Apple store is 35 miles away; there is an authorized service provider 5 miles away. I was told that this place would be happy to do the work for the regular amount to get a new battery because they chose not to participate in that program. So, I drove 35 miles to the Apple store.

You can contact Apple and let them know, but, as I said, an independent business can charge whatever they like. You should have asked when you took it in for service.

No, support can't help - you need to contact Apple corporate; unless they have a presence in your country, it would need to go with a regular letter to their headquarters in California (or call them there and ask for Customer Relations)

This is not the type of service that Apple is likely to charge for. In my experience Apple Stores have done courtesy repairs where no or minimal repair parts were needed, such as replacing a key cap or fishing a SIM card that my wife inserted without a tray. Or any kind of diagnostic service.

However, non-Apple service providers can charge for service. While Apple pays its own employees while they do free courtesy services, non-Apple shops don’t get reimbursed by Apple to do such work.

Could you rephrase the question please?

Did you charge someone for something? Or did they (a service) charge you? Who was the "service"?

Unfortunately, Apple does not publish their emails.