DiGi prepaid Bigbonus 28 has unlimited call to all network for RM28 only.

ntg to do with call plans. digi network has volte and vowifi for compatible phones.

VoLTE and VoWiFi is supported on Digi. But it also depends on what phone model you're using too.
What phone model are you using?

Is this plan unlimited calls includes all network?
Is it auto renewable after 30 days?
Any penalty if cancel the plan?

Yes it's unlimited calls to all network, except special numbers as usual.
And yes, it is auto renewable and your data can be rollover to following months as long the first attempt on renewal process every month is successful.

Special numbers that starts with 1300, 121, video calls all those...
If you usually don't call those special numbers, then just assume it as unlimited calls to all networks.

Yeah. Prepaid plans have no contract.

Can...
Just walk in to the nearest Digi stores.

It normal. telco blame bank. bank blame telco. check with bank first.

Bank will not want to take responsibility. Been there done that with Air Selangor (via JomPay and Maybank).
Paid the wrong amount to Air Selangor. Asked Maybank to stop the payment, they say cannot do anything, need to refer to Air Selangor. Long story short - Got my money back 2 months later.

One time also I accidentally subscribe to Unlimited calls via BOS. Called up DIGI and reported issue, they refunded my RM 5 within less than a week, and i get to keep the Unlimited calls for 30 days.

Shit happens sometimes. All you need to do is patiently follow up with DIGI.

can, if bank deducted but money didn't go through to merchant.

Have you tried this?
https://www.digi.com.my/switch-to-digi#