I had some amount of NEO in NEON wallet .. i check it now, i do it probably once a week, and i dont see my NEO ( NEO 0, US $0.00), but amount of GAS is still rising... so i assume this is only some bug in wallet, i dont have latest version..
Do you think this is my problem or my NEO has been stolen?
You are fine, I read about a bug in the NEON wallet on the reddit thread that does this. Remember you can always check the online exporer with your address to see your balance:
https://www.antchain.xyz/address/YourNEOAddress