I’m unable to download beta program

Have you tried this:

From your iOS device, go to beta.apple.com/profile to download the configuration profile. Your iOS device will notify you when the profile has been downloaded. Open Settings, tap general, tap VPN & Device Management, click on the profile and follow the onscreen instructions to allow installation.

Then to update you would open Settings, tap general, tap Software Update.

https://beta.apple.com/sp/betaprogram/enroll#ios-download

You’ll need to discuss the beta program and beta versions and issues with same with Apple.