Feeling Stuck After Resigning: How to Handle No Confirmation from New Job's HR?

I asked for an extension of the date of joining (DOJ) to my new company. They agreed, and after that, I submitted my resignation. Now, my new company's HR informed me of the joining date over a call and refused to send a confirmation email, stating it's not necessary. What should I do since I have already resigned from my current company? I am feeling very worried.

I don't have any official proof to enter the new employee office premises or the reporting time. Also, I don't know the exact details. Last time on call, the HR was very rude to me because I extended the date of joining; he was not happy at all. I am afraid that if he drops my candidature, I will be in big trouble.

Hello, why insist on an email if they've previously confirmed the date? Simply fulfill your notice period and report to your new polytrack.