Is everyone obligated to follow the fatwas of his country, and if we adopt the fatwas of scholars of other countries, is it considered a sin?

: It is permissible for one who do not specialize in Shari `ah sciences to apply the opinions of renowned scholars whom he trusts ,whether they be from his own country or not ,but if the scholars don`t arrive at a consensus concerning a certain matter then he must consult someone who is more knowledgeable than himself .It is preferable that you(the inquirer) specify the case of your interest ,so that we could give you a more specific answer since some scholars deliver fatwas based on atypical opinions which should not be applied no matter what .And Allah ,The Exalted, knows best.

What is the ruling on not fulfilling a vow?

A vow is a commitment towards Allah, The Almighty, and so, it should be observed as much as possible, and it is impermissible to take it lightly. Allah, The Exalted, says –in commending the believers-: “(Because) they perform the vow and fear a day whereof the evil is wide-spreading,”{Al-Insan/7}.

Is it permissible to fast on behalf of the dead who died owing missed fast to make up ?

His relative should fast on his behalf, and it is permissible for the guardians to give permission to non-relatives of the dead to fast on his behalf as well.

For passing time, my friends and I have called a famous diviner. She told me that somebody had cast a spill on me not to get married for the rest of my life. I didn`t believe her, but I can`t forget her words. How can I protect myself from such thing?

Praise be to Allah the Lord of the Worlds.

Dealing with diviners is forbidden and what you are suffering from is due to your having consulted that diviner. Have trust in Allah and ask Him for forgiveness, but rest assured that whatever Allah has decreed will take place. And Allah The Almighty Knows Best.