Ever hear of "autocorrect"?
Apparantly not.
Here, I'll give you some resources. Maybe you'll learn something. Probably not, you're pretty damn thick-skulled.
Autocorrect on Dictionary.com
Text replacement on Wikipedia
Now that that's out of the way, I can tell you that, after being an advanced iOS user for over three years, autocorrect often likes to think it's right when it's not. In fact, it's a well known problem that autocorrect gets things wrong quite often for everybody else too. Do your Google searching.
Do you know what an Input Method Editor is? Or specifically, how an IME for Japanese works? Let me walk you through it:
I type out "maiga", that is m-a-i-g-a, and it returns the hiragana まいが with a bold, black underline.
But "まいが" can mean a lot of things, and the hiragana is too vague on its own in this case. So, with the hiragana underlined, I press the spacebar to change it into a kanji.

Look at that, we're presented with what the computer believes to be our most desired set of kanji. You can see that if we press 1 we'll get the name "Mai" followed by the kana for "the", if we press 2 we get "My" followed by "the" again. Further down the list you can see things like the kanjis for "dance", "sheet", "rice", all followed by "ga". Now where is the elusive マイガ that we are after, the proper spelling of your name? Hmm... it's clearly not on the list, so it must be further down...

Oh look at that! The proper spelling is just the random assortment of katakana that appears at the bottom (notice the scrollbar) of every kanji suggestion after the computer gives up on trying to find your kanji. So apparently, this mythical autocorrect was able to read your mind, and choose the least-likely solution to your other-wise correct sentence fragment, and output the made-up name that you were after.
Stop lying Miga, it only proves your autism somehow.