Have you tried visiting local repair stores? (I'm sorry I can't fully understand your question, are you saying where to repair your phone or that the software of your phone isn't working.) I'd also recommend that since you're phone is discontinued that you should avoid going to official Samsung stores as they would most likely propose you get a new phone (assuming that's what you don't want)
Questions to ask yourself:
Has your phone been damaged in its exterior?
Have you installed malicious applications on your phone?
Is your phone updated to the latest update?
How is your phone's storage?
Where did you buy your phone from?