What do you do with recalcitrant repairers?

[Dante_Stella]

What's the correct way to deal with repair facilities that do not get the job done, never present an estimate, make out a bill, or return anything? When you've waited. And emailed. And called. And been told something would be done next week... for months. This is a big-name place.

For people who have experienced and resolved this, what's the lever?

Thanks,
Dante