CAN'T UPDATE MY MAC

I have a Apple MacBook Air (13", Mid 2019), Intel i5 Processor (8th gen) running Catalina 10.15.7

I've tried all the methods I could find to update the macOS versions like safe mode, bootable installer, wiping the SSD and reinstalling, Internet Recovery and even Open Core Legacy Patcher.

Still, I'm unable to update it, while using internet recovery by pressing option+command+r , it just gives me an option to reinstall Catalina only.

In every other method, the installer downloads the update and asks to reboot. Instead of completing the update after reboot, it just boots into Catalina only.

I can't even install the security update for Catalina because of the same issue.

When contacted Apple, they said that the Mac is unable to connect to the Apple servers to fetch the latest update and had to brought to a service center. But, I need it for my daily work and the service centre is also pretty far.

Is there any solution regarding this? Any help would be really appreciated.