[Buyer trying to cancel after the order was delivered]

No, Fiverr does not do anything to support their sellers in situations like this, even if they come to agree that a buyer needed a different service and you completed the work as outlined. I've experienced the same thing and it's frustrating as hell -- I'm leaving Fiverr as a result because it just isn't worth the time/effort when you can get screwed by any random person who just doesn't feel like communicating/collaborating/being respectful at all. 

I've had people change their request mid-delivery AND after delivery and if you don't bend over backwards to accommodate, it's YOUR loss. 

Such a mess. Sellers need better protections if this is going to be a feasible set up.