Welcome to the forum.
India is a medically sophisticated country and injection equipment re-use is rare. There was an instance reported in which a number of persons acquired hepatitis B due to used equipment supplied by an unscrupulous company, but to my knowledge that is the only instance. And it is unlikely any doctor's office or clinic routinely re-uses equipment. Even in India or other developing countries, there is little economic incentive for such cheating; injection equipment costs pennies. So I believe you overreacted; there was no need for HIV testing. (And anyway, if this concerns you, HIV is a much lower risk than hepatitis B or C.)
That said, your negative test result at 83 days is 100% reliable. My guess is you actually had a 3rd generation antibody test; I'm not aware of any 2nd gen tests that include HIV-2 (although I suppose such tests may exist in India). But even this doesn't matter. The difference in 2nd and 3rd gen antibody tests is in shortening the front end of the seroconvesion window -- i.e. the reliability of results before 4-6 weeks. All antibody test types are equally accurate after 6-8 weeks, with virtually 100% reliability (even though official advice usually is for definitive results at 3 months). Below I have provided the link to a thread that discusses this in detail.
Those comments answer all your questions, but so there is no misunderstanding: 1) Your negative result is conclusive; no further testing is needed. 2,3) See above and the link below. 4) See above.
Here is the link about window periods:
http://www.medhelp.org/posts/show/1704700
I hope this has helped. Best wishes-- HHH, MD