In the US? No, you actually do not need to pay for the service if you deem the quality of the output to be substandard. In particular with art, it's pretty standard to put in a non-refundable downpayment with the final payment due on delivery.

You only lose those rights in the contracts you sign (which, in terms of GPT, you've likely clicked through a T&C which waves all right to dispute or reclaim payment).

If you ask an artist to draw a picture and decide it's crap, you can refuse to take it and to pay for it. They won't be too happy about it, but they'll own the picture and can sell it on the market.

Sounds like you should negotiate a better contract next time, such as one that allows for revisions.