Error loading operating system

Yesterday I called into Apple support to get help with updating my software. I’m currently using 10.9.5 and I needed to update my safari so I could do my taxes. My system runs OS X Mavericks. The 1st tech I spoke to told me to erase my computer and to restart it holding down command, alt and R. She said this will allow me to connect to Apple’s server so we can update my computer. Each time we tried to reinstall Macintosh HD we got an error message of This item is temporarily unavailable. We tried numerous times and nothing. She put me on hold then never came back or called me back. I finally called back and spoke to a different agent only to realize the 1st tech should not have told me to erase my computer. I spoke to a senior advisor who couldn’t help me. Now my computer sat Error loading operating system. I’ve lost my work, my pictures and a perfectly useful computer before I called Apple tech support isn’t working now. Of course Apple doesn’t want to take responsibility for what has happened to me. Now I have to take my 20in screen computer to the Apple store which is 1.5 from my home. My daughter’s saved colleges apps and scholarship essays were on that computer. I’m devaste. If anyone in the community know how to fix this please help b/c Apple tech support has no clue. I’m not tech savy but I do use my computer for work so I’ll also be behind on my deadlines. Now I have to spend money I’m not prepared to spend.