It is better to inform the US consultate or office from which the visa was issued.
For International students pursuing studies in USA, the visa granted in F1. This is for any studies that involves more than 18 hours in a week.
The validity of a F1 visa is based on the 'DURATION OF STATUS' which is until the course completes. Once the course is over, the student has to leave within 60 days.
For issue of F1 visa, the US school/college/university issues a Form I-20, this is a student and exchange visitor information system (SEVIS) document that falls under the US department of homeland security.
In your case, the college that has issued the I-20, would inform the Immigration authorities about the failure of the candidate to join the course.
It would be wise to contact the US consulate that issued the F1 visa and inform by means of a detailed letter as to why the student is not joinings studies. This would be helpful, in case the student has to apply for future visas to USA for studies or work.
It is advisable NOT to travel to USA on the same F1 visa, even if the F1 visa is valid but the student is entering USA after the start date of the intended course.
Please inform the university also about the decision not to take up the accepted course.
I would suggest, use the contact information provided to you when you applied for the visa or please visit the (http://www.ustraveldocs.com/in/in-main-contactus.asp)
Phone: Call +91 120 4844644 or +91 40 46258222.