There's no setting that allows the hotspot app (whether it's part of Android or an external app makes no difference) to work, but other apps to not work. Possibly reflashing the ROM would fix the problem, or possibly there's a hardware issue. (And flashing the ROM wipes everything you've done since you got the phone, so you have to have
everything backed up.)
Flashing a Samsung is almost trivial, though - see
[Samsung] How to flash Stock ROM via ODIN. (And don't die of boredom - wait until there's a good TV show to watch while the phone sets itself up, or you'll be watching grass grow in the Arctic in the winter.)