i might just add, you should not double command a dog (so saying "come" for 5 minutes will only re-enforce bad behaviour) if you are being ignored you could try running away from the dog and turning it into a game (99% the dog should follow you) or if the dog is REALY stubborn hide behind a tree or building etc and dont come out, the dog will generally start looking for you after a while and when he finds you give the come comand and back away from the dog, when he reaches you treat and lots of praise.

good luck and keep us updated on your progress