My Son's Dad Keeps Changing His Visits Without Communication

I dont know that there's really anything I can do here.

I live in Indiana and I have full legal and physical custody of my 2yo. His dad keeps making up reasons he can't show up on the day he picked during the week. It's one day. I know he isn't at work, because we scheduled it around that shift. He says things like "I had to stay through 3rd shift because someone called off", "I'm helping someone move" (literally three days after I told his mom I was doing exactly that), "I've been sick all night".

I have to wait until he doesn't show up to realize he's not coming. He refuses to change his visit to a day he can manage. He just asks to change it after I text him to find out if he's coming, or he says he can't come and texts me two days later asking if he can pick up in an hour.

I don't have any experience with this. My son doesn't even look surprised anymore when I've gotten him ready to go and then tell him his dad isn't coming. At first it upset him. But it's now been at least four months of almost every week being rescheduled at the last minute and I can't plan anything for my son. Not a change in childcare, not visits with family members who have become more constant and reliable to him than his dad, not activities or leaving the house with my son at all without worrying he's going to ask for a make-up visit. I don't know if I'm legally allowed to refuse his requests, even at the last minute.