It's not necessarily considered them damaging it. If, let's say, while fixing it, they'd put another crack, then, yes, they'd have to fix it. But in this case their job was to stop the crack from spreading. And they can argue that they did. Yeah, it looks worse than before but they've never implied it's going to look like new. Similarly, if you hire a painter and he does a bad job, you cannot do that much about it. Vendors have a lot of protection. To make matters worse, even if you win small claims court case, there is no feasible way to make them actually pay unless you get a hold of their bank account number. If you'd pay with a check for instance. So try your best of course, but it's not clear cut by far.