Did Nikola Tesla receive "nothing but insults and humiliation"?

I see this quote pop up occasionally:

Nikola Tesla's last message to his mother: "All these years that I had spent in the service of mankind brought me nothing but insults and humiliation." pic.twitter.com/OmfbsC5GHR

— World of Engineering (@engineers_feed) July 25, 2021

But what's the source of it?

The most prominent source appears to be this article from March 2015 in Telegraf.rs. It is a series of letters purportedly written by Tesla to his mother just before she died. It contains the quote:

All these years I have spent in the service of mankind brought me nothing but insults and humiliation

But what's this at the bottom of the article?

Hmm... So, where did they get it from?

The only earlier work I've found for these letters is a post from January 2015 on the blog "SINESTETIČKI IMAGINARIUM".

The blog appears to mostly be poetry and other creative writing. The post claims to be the "first English translation of the last letter of Nikola Tesla". It contains such entries as:

Sunday the 22nd of November
This letter you will never receive, mother. I do not know why I am writing to you, the one who can never ever read this.
Rest in peace mother, and do forgive me that my roads brought me so far away from you that I cannot even come to your funeral.
I am reading the telegraph with the news of you passing away and I despise people who were not ready even two years ago to realise that electricity can be transmitted wireless. Now they saw it can be done but still they will not be able to use it for centuries, because someone has burned to the ground my laboratory in the centre of the town, with all my records and technical drawings.

There are a few problems with this.

The first wrinkle is that Tesla's mother, Đuka Mandić, died in 1892. The letters start on Wednesday 18th November. Which was a Friday.

(Although, as pointed out by Patrick Smears, Tesla's mother died in Croatia - which was still on the Julian Calendar. So, for her, it would have been a Wednesday.)

Most sources seem to agree that she died in April 1892. With Tesla travelling from America to Europe when he heard of her illness.

There's also the matter of the lab fire. Tesla's lab burned down in 1895 - 3 years after this supposed letter.

The book "Nikola Tesla, Correspondence with Relatives" published by the Tesla Memorial Society contains some of his surviving letters. The index of letters only has a few in 1892. None appear to be to his mother.

In his autobiography, Tesla says of the spring of 1892:

Imagine the pain and distress I felt when it flashed upon my mind that a dispatch was handed to me at that very moment bearing the sad news that my mother was dying. I remembered how I made the long journey home without an hour of rest and how she passed away after weeks of agony!

Later in the same book, he says:

But only once in the course of my existence have I had an experience which momentarily impressed me as supernatural. It was at the time of my mother’s death. I had become completely exhausted by pain and long vigilance, and one night was carried to a building about two blocks from our home. As I lay helpless there, I thought that if my mother died while I was away from her bedside she would surely give me a sign.
Two or three months before I was in London in company with my late friend, Sir William Crookes, when spiritualism was discussed, and I was under the full sway of these thoughts.
I reflected that the conditions for a look into the beyond were most favorable, for my mother was a woman of genius and particularly excelling in the powers of intuition. During the whole night every fiber in my brain was strained in expectancy, but nothing happened until early in the morning, when I fell in a sleep, or perhaps a swoon, and saw a cloud carrying angelic figures of marvelous beauty, one of whom gazed upon me lovingly and gradually assumed the features of my mother.
The appearance slowly floated across the room and vanished, and I was awakened by an indescribably sweet song of many voices. In that instant a certitude, which no words can express, came upon me that my mother had just died. And that was true.
When I recovered I sought for a long time the external cause of this strange manifestation and, to my great relief, I succeeded after many months of fruitless effort. I had seen the painting of a celebrated artist, representing allegorically one of the seasons in the form of a cloud with a group of angels which seemed to actually float in the air, and this had struck me forcefully. It was exactly the same that appeared in my dream, with the exception of my mother’s likeness.
The music came from the choir in the church nearby at the early mass of Easter morning, explaining everything satisfactorily in conformity with scientific facts.

I think this is fairly conclusive. Tesla had been lecturing in London in February 1892. A few months after that, he was with his mother in Easter. The Tesla Museum says:

Learning that his mother was close to death, he arrived in Gospic on April 15, just in time to say goodbye to the person he loved most of all.

After she died, he visited Zagreb in May 1892.

While we can never know how Tesla felt towards the end of his life, I think we can safely say that this "letter" couldn't have been written in November and is most likely a work of fiction. The "quote" is probably complete bunkum.