If you insist on canceling… there is nothing they can do, in some case it’s abusing the system. But if it’s justified (and be honest), I’ll just insist on cancellation and put the money on standstill, so the seller will never get the payment.
Customer support seldom take the side of the seller, I think majority of the sellers here will agree, I would love to take a look at the “before” and “after”… and your input on how many revision was done within “the few days”. Because it’s rare that CS takes the side of the seller, I’m incline to believe it’s justifiable.
You’re a buyer, I think you can probably show the design (but be prepared for scrutiny if other sellers here are fair in their judgment) but don’t dox the seller’s name.