He never hears what I’m trying to say.
The Japanese sentence is quite a confusing sentence to me; what roles does いたって play in this sentence? it does not seem to mean “extremely,” as is one dictionary definition of いたって。Takoboto | Word 至って, いたって, very much, exceedingly, extremely Then, does がたって mean something similar to にとって – “when it comes to me” or “regarding what I say” ?
Next, could you explain the 訳ないじゃない part? 訳 I believe serves to emphasize the first ない, as in “he never hears” – but what purpose does the following しゃない serve?
Re: いたって, the Kanji is not 至 (to reach) but 居 (to exist; be located). They are homophones and not interchangeable with each other.
私がいたって is a casual version of 私がいたとしても (even if I were there; even if I were on your side). It’s the same variation as in 私が言っても and 私が言ったとしても (even if I said to/suggested you so). Please note that we don’t usually spell いる in Kanji like 私が居たって. It should be written in Hiragana as the original Japanese sentence.
Re: 訳ない (or わけない), I have recently explained about a similar phrase わけにはいかない twice here and here. You can apply the same logic to わけない.
One of the meanings of 訳 is “rationale”. 訳ない or 訳がない (both sound natural), therefore, literally means “there is no rationale to reach such a conclusion or result in such a consequence”. If you may prefer free translations, “it’s impossible” or “no way!” is for わけない.
訳ないじゃない = 訳ない + じゃない = 訳ない + ではない(ですか？)
じゃ is phonetically contracted from です, では etc. じゃあ、またね！ (See you later!) is a casual version of では、また後で会いましょう！, for example.
So, 彼が言うこと聞くわけないじゃない is a casual shortened version of 彼が私の言うことを聞く訳がないではありませんか？ (lit. There is no rationale that he would listen to what I am saying, isn’t it?)