These two phrases mean basically the same thing and emphasize that the people refused to listen. AT: "They refused to listen" or "They refused to obey" (See: [[rc://en/ta/man/translate/figs-doublet]])
Jeremiah speaks of the people being stubborn as if they had made their necks stiff and unmovable. AT: "became stubborn" (See: [[rc://en/ta/man/translate/figs-metaphor]])