て済むことではない【てすむことではない】

て済むことではない turns down an easy fix: "~ing won't settle this", "this isn't something you can fix by ~ing". The verb in front is in the て-form, and it is usually the remedy someone is offering – apologising, paying, giving money back, crying.

すむ済む is "be settled", so the phrase reads "it is not a thing that is settled by ~ing". The negative goes on the end, not on 済む.

• × 謝る済むことではない → 謝って済むことではない

It is a rebuke, said in disputes, scandals and serious mistakes, and in speech ではない becomes じゃない. A second sentence often says why, or what should happen instead.

問題 and 話 in place of こと

すむ済むもんだい問題ではない and すむ済むはなし話ではない mean the same, and are at least as common.

After a noun

A noun or a quoted excuse takes で: で済むことではない. ではすまない済まない says much the same.