比较SQL Server中的两个日期（mm / yyyy）字符串

Okay, I have an issue I cannot quiet figure out and need some help. My clients offers payment plans and if often stuck with CC that expire before their payment plan. I need a way to identify those people for my client so they can actively contact them but I am having issues in comparing the two varchar columns as in I get false positives because it's a varchar.Okay, I have an issue I cannot quiet figure out