Pantech GF200 - Corrupt Memory

I bought Pantech GF200 last December When I was in Dubai. Somewhere in may-jun it gave problems. I lost whole telephone directory and the phone was showing " no enough Memory" . I was not able to access any of my telephone nos nor was I able to take photos etc. I visited Dubai again last month end and My friend took this phone to your service centre and problem was rectified. I am back to Africa after my holidays last week and again the phone is giving the same problem. Please adv how do I correc tthis problem.
I am able to receive and make calls that is it… Nothing else is possible. The moment I press phonebook, phone starts hanging .

Pls assist on this