Not given retirement after 15 year of service

1. I enrolled in IAF on 31 Dec 2008. Terms and conditions of Airmen prescribed in Air Force Instructions.12/s/48 issued by Govt of India, was in vogue at the time of my recruitment. 2. Terms and Conditions of engagement - Para 12(a) of AFI 12/s/48 stipulate that "Candidates will be enrolled initially for 20 years 'regular service' but those who fail to attain the rank of Corporal within 15 years will be discharged". At the time of my recruitment I was bound by this AFI. All Airmen who did not get their corporal rank within 15 years had got discharged on completion of 15 years of service as per this AFI. 3. Now the Govt of India has changed Terms and conditions of Airmen in Sep 2019 via AFI 01/2019 dated 02 Sep 2019. In this AFI, para 11-Terms of engagement states that "All candidates shall be enrolled for 20 years of regular service. The period of engagement shall be reckoned from the date of enrollment." 4. Till Jul 2020, all Airmen were got their discharged who fail to attain rank of Corporal within 15 years of service even after implementation of new AFI 01/2019. 5. Now based on new AFI 01/2019, IAF stopped discharged of Airmen who fail to attain rank of Corporal within 15 years of service stating that "AFI 01/2019 stipulate that Airwarriors who do not attain the rank of Corporal are to serve for 20 years" . However in AFI 01/2019 issued by Govt of India, neither such wordings nor this type of rule/conditions are given for Airmen. 6. Apart from that, the Govt of India changed Terms and Conditions of Airmen by AFI 01/2019 which was issued and came into force from 02 Sep 19 and did not even exist at the time of my recruitment. so please advice me for getting discharge from the service after 15 year, as per rule at the time of my recruitment.