What's the English equivalent for the German term "Salzamt", used when it's not possible to appeal a decision, or it's simply useless to complain?

A close phrase in English is to tell them to go pound sand. We don't have a government agency though.

The closest English equivalent to this expression is complaint department (occasionally complaints department), sarcastically referring to a fictional agency which responds to complaints.

For instance, you could say:

• Take it up with the complaint department.
• I'm not the complaint department.

Dear Points of View, Why, oh why, oh why, oh why ...

or

Dear BBC, Why, oh why, oh why, oh why ...

In the 1960's & 70's there was a BBC TV program called Points of View. It was designed to allow the public to express their views on the British Broadcasting Corporation's Television programmes, however it was clear that nothing that anyone complained about ever caused any change in the BBC's programming.

I still occasionally find myself muttering "Dear BBC ..." when faced with a situation where I know complaining will make no difference.

Here is a link to Wikipedia Points Of View It seems that the show is still on air some 50 years since it started and the BBC probably haven't acted on a single complaint in all those years.

I think I might send them a letter...

Catch-22 is close to what you are looking for, except that it has a specific reason why it is useless to complain or fight a decision.

The phrase comes from a story by the same name that explains a catch-22 as a situation where fighting or appealing something yields the same result as if you didn't fight at all. The story specifically describes the 22nd clause in some military terms where you can appeal for dismissal based on mental inability to perform your duties. The clause requires that you must make this appeal on your own volition, however, doing so proves that you are mentally capable, therefore, your request will be denied.

In usage, the phrase is sometimes simply said after it becomes clear that there is nothing you can do. Other times people who already understand will start with "It is a catch-22."

There is another phrase that means close to the same thing as catch-22: Screwed if you do and screwed if you don't. That's pretty self explanatory.

Most of the answers here so far are things I've never heard before as an American living in Iowa, Texas, and Colorado, although they may be regionally popular or popular in other English speaking countries.

I can't think of any phrase that is truly equivalent to what you've outlined, but there are a number of them that are close. I think the "no use in complaining" part will be easier than the "decision can't be repealed" part.

I think it would really help a lot if you provided some context or example situations where that phrase would be used.

Some possibilities:

"It is what it is." This means that things are as they are and can't be changed so there's no use in thinking/complaining about it. Just accept and move on.

"No use crying over spilled milk." Generally, means that there's no point in lamenting things you can't change. Also sometimes used when someone is complaining about something unimportant, like spilled milk.

"All decisions are final." Not even an idiom, just exactly what it says.

"I'm not the complaint department." As Theodore Broda suggested, this is really pretty close. There's no such thing as a complaint department.

"It's like talking to a wall." If you were trying to get a bureacrat to help you, and they weren't even really listening, this would be an appropriate thing to say to someone else in line. This phasing isn't specific. "I may as well talk to a wall," or some other variation would also be reasonable.

"Like arguing with the wind." This is similar to the last one.

I'm not English, but I have an English-speaking wife.

If I gave something to somebody and didn't want complaints about it, I'd just say,

There you go, take it or leave it.

In my opinion, this would function the same way as your phrase.

Your complaint will promptly be placed into the circular file (trashcan).

Consider Department of Hopeless Causes, Department of Lost Causes, Department of Last Chances, and Department of Last Resort.