Not providing relieving letter by HR

I am employee of hdfc life since 4 yr.On 14 sept.2021 I resign and by default got my last working day is 13 oct.2021 as I have to serve 30 days notice period,my reporting manager accept my resign on same day and amend my notice period of 30 days into 15 day and relieve me on 30 sept.2021 and he got mail from HO office that resign is approved and my last working day is 30 sept.,my circle head and HR are also in CC in related mail. On 30 sept.my reporting manger again mailed me approving my relieving and again HR in CC and behalf of this mail I had joined new company.but after relieving my official mail id and other IDs was still active so I inform my reporting manager .He discuss with HR about the issue ...Now HR told me that how I joined other company without his approval and threatend me to terminate me for dule employment....after several request they did not support me and frequently harass me. I had informed this issue with New company HR but they told me to I have to be submitt the relieving letter of 30 sept 2021.if I failed to do so they are going to terminate me also. So please advice me what should I do....where I have to filed complaint against the HR and company.