Couple of quick thoughts
- (Assuming USA) some places also have local/state rebates
for both For both Federal and local rebates... your concern should be if contractor claimed those rebates and took that money as well (and that may well not be Fed or local agency responsibility)... you probably need to get a lawyer involved (ideally one familiar with residential construction, though commercial building construction is similar enough if need be)
Another possibility, if you can find one, is a competent local solar system master/certified electrician inspector... someone who can go over your install with a fine-tooth comb (so to speak) and identify any potential issues. In my case, with significant issues found with my install (but not the horror stories other's have had), the inspection money spent will reduce my bill to the contractor (if project ever completed, and any amounts ever due... other discussion).
Such an inspection report, I'll also be using for a contractor license board complaint. The process and requirements for such a complaint depend on your local jurisdiction.
Such an inspection report will also inform you of what anyone else may need to remediate in order to pass inspection. And then there is tracking down what, if any, applications submitted to AHJ (local housing jurisdiction), Power Company (PoCo). And that info will then determine what all will be required to get your system permitted, inspected (if applicable) and operational
*IF* your contractor has filed bankruptcy, that has one set of implication. if not, time to get a court judgement against that person/company. including job abandonment. Sometimes pursuing such gets contractors to re-engage (but not something to expect).