They stopped hiring for the position I was interested in because they already had a sufficient number of applicants.
They are no longer accepting applications for the position I was interested in because they have already received enough applications.
英語は日本語ほどへりくだりはないのですが、解答1も解答2もフォーマルな言い方です。もっとカジュアルで言いますと “They aren’t hiring for the job I was interested in anymore because they already got enough people.” “position” も “job” も仕事の事ですが、 “position” の方がフォーマルな言い方です。 “have” も “got” よりフォーマルになります。