I with family and friends went for dinner to this Indian restaurant. We received appetizer after 30mins (that's fine for me) and main dishes after 45mins(even that's fine for me as well). While we are about 80% of the main dish, the waiter brought two more dishes, which we have not ordered. I said - sorry they have not been ordered for this table!
Later the manager came and started insisting. I just let it go. At the end during payment time, he charged those both dishes which showed up on the bill (i repeated, i and none of my friends ordered them). I said you can charge one of them but 2nd one, i can't. Then he removed the second one from the bill, and when i received another bill (updated), i saw GRATUITY 20% being already charged in the total bill, which is around 20+$.

I asked why you are giving tips by yourself, it should be done by the customer. He replied "if there are more than 4 people in a table, we do that". I asked "where is the rule written in the US?"  he replied "our computer machine does automatically".

I simply paid and left  saying "we did not get good service and this is not the way the customers should be treated"
(it was my kid's b'day today, and we did not want any  unnecessary environment to be created there)

(there were not many cusotmers either; when reached around 730pm, there were only 5 tables being occupied and later just ours and another)

First of all I paid 14$ for the dish I or none of my group members ordered it   ===> i can consider this as assuming the waiter misunderstood us while taking order. That much of money was not too big for me either, however, I am simply upset by his behavior and that 20% tips already charged(???)

my main concern is 20% GRAUTIY fee and  that guy's behavior. 

In this situation, what would you have done... How can it be reported and where? or whether it is good to report to police? or forget this matter??

 The best thing to do will be to just let it go and never visit the place again.
And you can also write this story in the restaurants review--give them a bad review.

Apart from the 2 wrong dishes brought, the gratuity charge sounds fair because I have seen many restaurants do that for a big number( which in their case was 4). Btw with the gratuity charged, you could have adjusted your tips accordingly. Anyway, if you don't like the place and to report, just leave a bad review on yelp and other sources were the restaurant might be listed online. That should do the damage

Gratuity charge is pretty common. It is usually mentioned on the menu etc.
Can u tell us about the place. So that we don't end up there!!!

I read this story, a police was involved because the customer did not pay 18% gratuity and the restaurant owner called the cop (not an Indian restaurant).

 it is a common practice to include gratuity charge for a large party greater than 4 but 20% sounds a little too much. 
if you did not order, you have the right to cancel and refuse to pay. stand up for what is right..dont hesitate that people around will feel that you are cheap. your kid (assuming he is old enough) could have learned a valuable lesson had you stood up for the right cause by refusing to pay!

come on man, when are we nepalese people going to stand up and stop being shy??

Yetro bhane pachi aba restaurant ko naam ra address pani ta bhandeu.