Hi

Eligibility criteria says that to be eligible  for JEE mains 2021 for BE or Btech you just must be either appearing for 12th board exam or equivalent  in 2021 or should have passed it in 2020 or 2019 with Physics,  mathematics and anyone of Chemistry or Biology or Biotechnology or Technical Vocational Subject

So, as per your 12th qualification you are not eligible for jee mains anymore as you have passed it in the year 2017 according to which you were eligible for JEE mains only till 2019.

But yes,

3 year diploma is equivalent to 10+2 , and as per eligibility criteria of jee mains, students with Diploma recognised by AICTE or recognised by a State board of technical education of at least 3 year duration are eligible for jee mains examination.

so, now that you have completed your 3 year diploma in 2020, yes you were eligible for JEE Mains 2020, and yes you are also eligible for JEE mains 2021 and 2022 with your diploma qualification.

For details visit the official page at

https://jeemain.nta.nic.in/WebInfo/Handler/FileHandler.ashx?i=File&ii=256&iii=Y#:~:text=Only%20those%20candidates%20who%20have,Main)%20April%20%2D2020%20Examination.

Thankyou