Visitor Visa - B2

MY VISA IS REJECTED ...PLEASE CAN ANYONE HELP ME.. WHAT IS THE REASON BEHIND THIS REJECTION...
OFC - 9/04/2017
Interview date: 10/04/2017
Morning: 8.30 AM appointment
we went inside around: 8.15AM
Interview around : 8.40AM(APPROX)

Hello Everyone , I am 24, female... I applied for B2 visa.. Currently ,my husband is in F1-OPT.. His graduation on May 2017. So, to attend his graduation ceremony I applied as a family (Me, Father-in-law mother-in-law) and got rejected. we are very much disappointed .. At least my in-laws would have got Visa approved.... I don't know why parents are also getting rejected...
 
   
Vo: Good Morning( vanakkam) (very bold voice and rude man.. his Tamil accent was very good)
Me , FATHER-IN-LAW & MOTHER IN-LAW: replied Good Morning Sir..

**** **** **** **** **** **** **** **** **** **
VO: Whom r u going to see? Neengal yara pakka pogirirgal?(tamil)
FATHER-IN-LAW: I am going to see my son...Naan en magan ah pakka pogirom(Tamil).
VO: Do you have Property? Unkagaluku Property iruka ah??(Tamil)
FATHER-IN-LAW: "Yes" iruku
VO: What r u doing here? (Occupation) neengal inga enna pandringal(Tamil)
FATHER-IN-LAW: I am a Business man... Naan Business pandran..(Tamil)
VO: what type of Business? Entha type of Business ?(Tamil)
FATHER-IN-LAW: Export Business
VO: Which type of Export Business doing? Entha type of Export Business pandringa?(Tamil)
FATHER-IN-LAW: like Spicy items, groceries, hardware items...etc blah blah...
VO: how many days r u going to stay? .. ethana naal stay panna poringa?(Tamil)
FATHER-IN-LAW: 3 Weeks
VO asked to MOTHER-IN-LAW: what r u doing madam Neengal enna pandringa madam?
MOTHER IN-LAW: Tensed and said House Wife.
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Then suddenly he (VO) turned at me and questioned me in English...

VO: Hey.. What are you doing Here?(Occupation)
ME: Replied as I am working in XYZ company
VO: What's your Salary?
Me: I said my salary is Rs.10,000 per month(he was entering something into system)
VO: what is your husband doing?
Me: he finished his master's and Currently in OPT
VO:(he was typing.. typing.. typing..) currently where is he staying ?
Me: replied..... He is Chicago, Illinois..
VO: which university did your husband studied?
Me: California University of Management and Science.....typing again
VO: why do you not applied for F2 visa ??
Me: because, I am working here... I don't have any idea to resign my job here and go by F2 dependent visa...I would like to attend my husband Graduation ceremony and then return back to India.

VO: suddenly VO end his speaker and then he went inside to ask to another person..we were nervous and our heart beat was beating faster......

VO: he came and sat in his seat and ON his speaker... R u in Training?
Me: was (nervous)...I replied "yes"...
VO: he asked how many months training ?
Me: replied as... 6 months.. I finished my training ..
VO: then your salary been increased after training??
Me: ..Yes definitely they will increase by next month. but they did not mention anything as of now.

typing .. typing ... typing.. something
 
VO- FATHER-IN-LAW: (Suddenly).. Ungaluku oru magan than ah ??
FATHER-IN-LAW: (he didn't listen properly).. he told to repeat again..like ahhh?
VO: suddenly VO faced at me
Me: I said Yes only one Son..

VO: he took one paper from shelve and said this time i cant approve ur visa..... ungalukku intha murai VISA thara Mudiyathu ..
FATHER-IN-LAW: got tensed and asked sir ???
VO: he faced me and said UR VISA is REFUSED... (without any proper reason)
VO: he did not look at our faces .... he just called next ..come on....

Actually VO didn't not asked proper question... VO thought we r going as a tourist to visit place and to see the son who is in the USA... VO didn't ask for any documents..
we were shocked and came out from embassy sadly...
please can anyone help me what's the reason and when can I reapply again... In my case ... VO thought that her salary is less... or something what gone wrong .. I don't know guys...