Should I pay the mastering engineer in full even if it sounds horrible?

I'm getting a project mastered, and the first revision came back sounding quite a bit worse than the mixes. It was very harsh, messy, and there was a lot of distortion that wasn't there before. The bass and kick drums were maxing out and tearing ect. and interfering with the other instruments. It's like they mangled it.

My guess is that they didn't even really try or outsourced it to an amateur, as the previous master was great. I asked for a revision removing these issues, and it came back more or less the same.

I'm trying to work with them to get it fixed, but I do not have faith they will be able to fix it considering what they had the gall to send me twice now lmao

Do I pay them in full anyway even if the final product sounds atrocious? I would feel bad if I didn't pay them, but none of it is usable.

Update: Thanks for the advice everyone. I'm asking for more revisions, and paying them even if doesn't work out in the end.