Getting Yosemite instead of El Capitan
I think You should make clean install of El Capitan from USB. You were not scammed, don't worry. I was in the same situation.
It can be done under one condition - You've updated somewhere in the past to the El Capitan and You can see it in Purchased section in AppStore.
That's nothing complicated, first make sure that You have downloaded El Capitan from AppStore. Than You should make bootable El Capitan USB and clean-install it on Your Mac. Follow these steps on this site:

http://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html