Hello Aspirant,

First of all, don't be discouraged by this all this. The positive thing that happened is that you got selected for a job according to your qualification.
BPP or Bachelor's Preparatory Program furnished by Indira Gandhi National Open University is a course an individual can do before a graduation course. This is for the students who have not passed 10+2 and want to do graduation. This course is for 6 months and can be extended up to 2 years. There are several BPP courses in subjects like Social Sciences, Commerce, Science etc. I have to inform you that this course is not at all equivalent to a 10+2 level. The company in which you got the job might be looking for someone who had done 10+2 in any stream. So, they might have rejected you for this. BPP is adequate and acceptable for some jobs. But most authorities look for a student who did complete his 10+2. They want someone who has done 10+2+3 level. You don't need to worry you can give your class the 11th and 12th exams in private or in distance mode also. NIOS or any other valid board from your state who furnishes this can come to your rescue.
NIOS is a very distinguished Board of education as CBSE or ICSE. It gives school education through distance mode. You can choose this under several subjects. You can also prefer the stream you like.
Application payments
Exam payment- INR 250/- per subject.
Additional payment for practicals in subjects possessing theory and practicals - INR 120/- per subject.

For admission, click here
http://112.133.209.200/onlinehome.aspx

NIOS authorized web address -
https://sdmis.nios.ac.in

NIOS also has a policy of detailed online acknowledgements.
Aadhaar card or passport or ration card or other identity proof.
Birth certificate for proof of date of birth
Address proof i.e. Aadhaar card
Signature ( must be in black ink)
Current passport size colour image
class 10th marksheet
Disability certificate for PwD candidates
Caste certificate for SC/ST/OBC candidates.
Ex-serviceman certificate for aspirants under the Ex-serviceman category

To know more click
https://school.careers360.com/exams/nios-class-12

Regards.