Macbook Air hardrive fail problem

Hi, I would like to ask for some help. A few days ago i took my (15 months old) Macbook Air to the Apple representative in Uruguay (I'm here travelling) because the general password was not being recognized so i wanted it to be reset. They did that and the next day I picked it up from them and used it all day. In the evening it suddenly froze while i was using it. I turned it of and back on and it started displaying a sign of a file with a question mark on it. I took it back to the shop the next day and left it with them. They were supposed to call me that day but never did. the next day I called them and they told me that the computer was not recognizing the hardrive, that there was a hardrive failure, that reparing it would cost much more thsn the cost of the machine itself so i needed to buy a new one and that on top of that they could not recover any data. Everything is supposedly gone forever. I asked if there was nothing they could do to recover the data and they said " we do not have the technology to do that"...

More worrying they told me that the hardrive inside the machine was not the original. I opened the original box myself and the laptop has always been with me, never serviced or left for a prolonged amount of time outside my reach.

After that they told me that they were going to look at it again and they were going to call me when it was ready

I told them that i was travelling that evening. They never called back. When i tried calling them no one picked up, it was closed. It was a Saturday, the dont open Sundays so I had to change my ticket and stay untill They opened again.

Please guys help me because i don't know what to do. I'm not a very technical girl but this all sounds a bit strange to me.

Plus I lost very important data that i need for my work that i need to recover.

Can you please suggest what i can do?? I would greatly appreciare it!!!

Thank you!!