Hi azargoshtasb,
First off, a 670/Q50 is a strong score (it's above the 80th percentile overall), so it could be enough to get you into your first-choice School. As such, a retest might not be necessary. Depending on the Schools that you plan to apply to, you would likely find it beneficial to speak with an Admissions Expert about your overall profile. There's a Forum full of them here:
ask-admission-consultants-124/Your Official Scores are remarkably consistent, which means that you're treating the Exam in the same general ways every time you take it - you do certain things consistently well, but you also make the same consistent mistakes. Since you now have 3 Official Scores that are essentially identical, you should not plan to take the GMAT for a 4th time until you've made some significant changes to how you handle the Verbal section of the Exam. There might also be aspects to Test Day itself that you are not properly accounting for during your studies, so changing how you train for every aspect of that day might also be necessary.
1) What is your goal score?
2) When are you planning to apply to Business School?
3) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich