Yeah, it's never a good idea to have a seller do a repair. Never. They are always going to do it as cheaply as they possibly can. It's always better to get your own estimate to correct the problem, and then ask for a credit at closing so YOU can have the repair done right once you own it. Or you could have had their work inspected before closing. Even then there are no guarantees, and there are usually hidden surprises once repairs begin.
I'm sorry you are dealing with problems though. Hopefully it's nothing too serious.
You might have a chance in court though, if you can prove they lied and faked a receipt....and then have it done right yourself. Or better yet, have your lawyer send them a letter and ask for them to do the right thing and give you some money back....Going to court absolutely sucks!!
There are almost always a few hidden surprises on any house, even a brand new one.