Apple Support messed up my Macbook

I have been using my Macbook 12inch for 5 years and it's been working great. Until recently I ran into some issues with the Macbook and it would just automatically shut down. I brought it to Apple Store for repair and diagnosis and they couldn't find what the issue was. When I brought the macbook home I found that Apple had uninstalled the MacOS setup and for some reason I could not reinstall it. I brought it back to Apple but even they couldn't reinstall MacOS, therefore making my Macbook an empty computer with no working software. I complained to Apple about it and they only said it could be an issue with my Macbook hardware and they could not do anything about it. My main concern here is that for one, I brought in a "WORKING" laptop for repair and brought home an empty computer without any working softwares. And for two, there is no evidence indicating why I can't install MacOS on my Macbook; whether or not it is a hardware issue or a manmade error . And I think it is reasonable to suspect improper handling on the part of Apple technicians at this Apple Store location.