If I could rate them 0, I would

Everything seemed great until they started doing my installation. Cables are a mess, they installed the wrong thing, installed it in a different place from where we agreed, caused damage in moving it to where we agreed. They told me they couldn't leave until they'd been paid, and that someone would be back to fix the damage caused and correct the cable installation. I refused to pay them in full, paid half and said I'd pay the rest once they'd fixed the issues. Now that I try contact them to ask when they'll have someone fix the issue, they say that it's my fault, tell me that I changed my mind as to where I wanted the installation done, that they can't fix it (and that they don't even know how to), and that it's an expected consequence of installation. I'm very curious as to how they think paint damage on a wall 1.2 metres away from where they were meant to be doing anything is an expected consequence.