What to say when they won't plan a date or repeatedly cancel

What to say to someone who never makes firm date plans, or repeatedly cancels dates last minute. This person will frequently say things like:

• "Let's decide on the day of..."
• "Can we reschedule today's hangout?"
• "I'll let you know by Tuesday whether I'm free to meet up..."
• "Let's say Thursday for now but I'll confirm closer to the date.."