Whenever I confronted him about the unpaid bills, he promised to handle it.

confronted 是动词 confront 的过去式，confront 由前缀 con-（表示"共同、一起"）和词根 front（"前面、面对"）组成，意思是"面对、对质、质问"。confronted 在这里表示"过去曾经质问"的动作。