Bro don't bother going to KSL or City Square Digi, they only want you to spend more. Never stepped into the shop for years.
Retail price for SIM (RM5 credit preloaded) is RM8 and nothing more. You should not be forced by the shop to do a credit top-up just because you want to buy a SIM card; which the shop always tells you that SIM card will cost you RM2x or RM3x and they don't sell SIM only b***s***.
I'm quite sure your Digi prepaid sim still works, just have to top-up every other month and activate a data plan (don't exceed 90 days if I'm not wrong).
Try download the MyDigi app, it's easier to manage and top-up that way.
There are 2 types of data plan - Auto Renew subscription or One-time pass. If you don't use often, I would suggest to just purchase one-time pass which would be sufficient for most - e.g. RM3 for 3GB valid for 1 day. RM12 for 4GB valid for 7 days, etc...
For the cheapest 1-2 days plan, check out the Box of Surprise. I can purchase 1GB for 2 days @ RM1.50.