I suppose where you stand depends on a number of different factors - the first one is what does it say in the contract? Perhaps you have a legal leg to stand on if the design work is noticeably poorer than from what is in his portfolio
You should have seen their samples before giving them the project. As skill leave impact on designs. anyway, feeling bad for you. How much have you paid them ?
Don't waste any more time with these guys! Nothing good will come out of dealing with them except wasting more time and headache. Good luck.