A few months ago (September) we had some new granite worktops installed in our house. The same day, the installer also fitted some at MILs (I arrange both installations as I was overseeing her kitchen refit for her.)Less than a week later, our worktop cracked along the join. As we discovered, the installer had fitted the worktop with a join over our integrated washing machine - the join was floating, no support at all, no cement etc underneath, and he'd also not used any silicon or adjusted the unit legs to the right so it was unsupported for about 1m.
He initially said he took responsibility, came out and attempted a fix which was hideous and which we said wasn't good enough. He then said he'd send a specialist who was anything but who did another really shit job. A toddler could have done better with crayon. He also didn't install the sink which he was supposed to install and which was included in the quote, so that cost us £150 (weekend) cos he left us at 5pm on a Friday with no damn sink! 
We've been trying to get it sorted with the installer ever since. He refuses to accept responsibility claiming that our painter "must have" stood on it (possible but not likely and not the cause of the damage, that would be his botched job) however the worktop actually moved under my hands - so just leaning on it made the right hand side flex up and down IYSWIM? It's the busiest possible spot in the kitchen, exactly where you tend to dump heavy bags of shopping, that kind of thing.
Then he started demanding payment (because it broke so damned quickly we hadn't actually paid yet). We've been trying to come to a reasonable agreement - we asked him to replace them, nowt. We eventually got out own joiner to come and support the units and got a cosmetic repairer to come and fix the surface. Meanwhile he offers £200 compensation (£2.3k worktops, aye right!). We countered with £200 plus our costs, making for a total discount of about £600. Seemed reasonable to us given the mess he'd made but hey (there were other fitting mistakes too)
This has been going back and forth for a while, but today he has emailed MY MIL!! Telling her to"please ask Stat and Stats DH to pay their bill", informing her that we have asked for a £600 discount, a few other details, and then telling her that if we don't pay up he's going to speak to a solicitor!
I'm fuming. How utterly unprofessional can you get!
(incidentally, he actually did the same at MIL's house, she has a floating unsupported join too. We didn't notice until after her bill was paid)