This is a poetic device. It does not mean that a specific number of sins had been committed, but indicates that many sins had led to God's judgment. See how you translated these words in [Amos 1:3](../01/03.md).
Yahweh uses two negatives here to emphasize that he will punish them. See how you translated these words in [Amos 1:3](../01/03.md). (See: [[rc://en/ta/man/jit/figs-litotes]])
This expression here probably refers to worshiping false gods or idols. Alternate translation: "Their worship of idols" (See: [[rc://en/ta/man/jit/figs-metaphor]])