Why don't you subscribe to the long life plan.  It cost you RM30 a year.  No need to top up every month.  It last you for one year.
Only top up on your birthday. You top up RM30 and get RM15 free talk time.

You must be in Digi Best Hit Plan then only you can subscribe to the long life plan.
If you have RM500+ in your credit, once you subscribe to long life plan, it will deduct RM30 from your credit. The rest of the credit you can use until the one year is up.
So, next year before the long life plan expires, you subscribe again and RM30 will be deducted from your credit.
Usually people will top up during their birthday and you get additional 50% in your credit.

Changing plans may cost you a few RM.
Don't worry, the credits are still there as long as you did not use them.

The convenient way is to go to a mobile phone shop and ask them to do it for you.
If they said Beyond cannot subscribe to long life plan, then ask them what to do next.
Check your balance first before they do anything.
After done, check balance again to see if the amount deducted is correct.