I took my mac mini in to a computer repair shop, they said I needed a new hard drive, so I paid them $300.00 to do the repair. Later on when I went to set up my mini mac it wouldn't work, and I found out that they replaced my apple hard drive with a toshiba hard drive. why would they do that
Yeah it sounds like maybe you just need to install the OS onto it (I guess "it wouldn't work" isn't really defined, so this is a guess).
If Tetsujin's suggestion doesn't work, and you have the older Mac Mini (I know my Mac Mini had the drive die - and it's from 2005, so internet recovery wasn't available), then put a Mac OS CD in the drive and boot up while holding down Command + C to boot from the CD drive. Then install the operating system from that.
You might also want to make sure the shop gave you back your old hard drive, since it has all your stuff on it. Depending on how dead the drive is, you could put it into an External Enclosure and try to get some of the data off it. (Make sure you choose the correct drive connection: IDE (older computers), SATA (newer computers I think?), or other types (mSATA etc.).
Apple don't make hard drives & it doesn't really matter who made it, so long as it's correctly formatted for the computer.
For $300 I would have expected the store to at least format it put a clean OS on it - that is a lot of money for a simple HD, which cost about $40 per terabyte these days.
$300 would buy you a 1TB SSD drive.
To get a basic OS onto it now, you need to boot it & hold Cmd ⌘ R at the chimes, which will allow you to use Internet Recovery.