Cognizant — Regarding Offer letter rejection

Hi,
I have received an offer which I was supposed to onboard on 27-Oct-2021 but HR called me on 26-Oct-2021 and told me that I got negative report during BGV process.
She did not give the exact reason for the negative and revoked the offer.
Today (8-Nov-2021) I received a call from your onboarding team asked about my joining?
So Could you please elaborate the exact reason for revoking as the onboarding team asked me to contact you and they were asking me the reason/issue?
Kindly Please reply ASAP.
Candidate Name : Ravindranath Gurram
Candidate Id : 18174825