Well, we do love @hawk too. She used to be our forum administrator a while ago
I know that the difference between $3500 and $2100 can seem significant to you but for me, it is not. Although I haven't seen the quotes so I'm not quite sure what company offers. Or their quotations.
So, with no further information, the fact that the first company qouted $1400 more than the other means nothing to me.
I would say that it is even cheap if they were really hand-conding. Which, as you say, it might not be true.
The fact that you needed only 15 min to create what they needed days to do, again, means nothing to me. It is obvious that you used a template which looked the way you wanted and it was already similar to what you were looking for. But quality coding, even if it is based on an already existing template, takes time. And there are many factors involved to be taken into account.
And I swear that it is not easy to look at someone else's code. Sometimes it is faster to do it yourself.
Having said this, you feel scammed and you don't trust this company. To me, even if your reasons were not real (which it is hard to know at this point), your distrust is reason enough to go somewhere else.
Recovering your cash is another matter. Because it depends on the contract you have with this company, first. Also, if you both live in the same country with the same rules.
It might be hard to base your case on the code itself, and the "fact" the they're cheating and copying code from somewhere else. But if you had a firm agreement on time and schedules, you might go from there. Obviously, if they have delayed the project a week or two, that might be reasonable. But if they indeed are taking too long and are over those 4 weeks for, let's say 7-8 weeks, you can complain that this company is not complaying with their end of the agreement.
I would advise to ask a lawyer, though. Because if you've hired this company through a third party like Upwork, you will have to take into consideration your agreement with this company and also Upwork's own terms.
The lesson for the future is... make sure that you do your homework and do a proper investigation before hiring a company.
I suspect that I haven't been of much help but I do feel your pain.